diff --git a/package.json b/package.json
index ebab08c..549b0fb 100644
--- a/package.json
+++ b/package.json
@@ -56,6 +56,7 @@
   },
   "devDependencies": {
     "@types/async": "^3.2.7",
+    "@types/atom": "^1.40.11",
     "@types/express": "^4.17.13",
     "@types/first-mate": "^7.0.6",
     "@types/fs-plus": "3.0.2",
diff --git a/src/apm-cli.ts b/src/apm-cli.ts
index 9069d3b..3a9f201 100644
--- a/src/apm-cli.ts
+++ b/src/apm-cli.ts
@@ -114,8 +114,10 @@ const commands = {
   show: viewClass,
 }
 
-function parseOptions(args = []) {
-  const options = yargs(args).wrap(Math.min(100, yargs.terminalWidth()))
+export type CliOptions = yargs.Argv<{}> & { commandArgs: string[] } // TODO pass commandArgs directly
+
+function parseOptions(args: string[] = []): CliOptions {
+  const options = yargs(args).wrap(Math.min(100, yargs.terminalWidth())) as CliOptions
   options.usage(`\
 
 apm - Atom Package Manager powered by https://atom.io
@@ -141,7 +143,7 @@ Run \`apm help <command>\` to see the more details about a specific command.\
   return options
 }
 
-function showHelp(options) {
+function showHelp(options: CliOptions) {
   if (options == null) {
     return
   }
@@ -266,7 +268,9 @@ function getPythonVersion(callback) {
   })
 }
 
-export function run(args, callback) {
+export type RunCallback = (error?: string | Error | null) => any
+
+export function run(args, callback: RunCallback) {
   let Command
   config.setupApmRcFile()
   const options = parseOptions(args)
@@ -276,7 +280,7 @@ export function run(args, callback) {
   }
 
   let callbackCalled = false
-  const handleErrorCallback = (error) => {
+  const handleErrorCallback = (error?: string | Error) => {
     if (callbackCalled) {
       return
     }
diff --git a/src/apm.ts b/src/apm.ts
index 1cf6570..e6c2e52 100644
--- a/src/apm.ts
+++ b/src/apm.ts
@@ -184,7 +184,7 @@ export function visualStudioIsInstalled(version) {
   }
 }
 
-export function loadNpm(callback) {
+export function loadNpm(callback: (config: null, npmVar: typeof npm) => void) {
   const npmOptions = {
     userconfig: getUserConfigPath(),
     globalconfig: getGlobalConfigPath(),
diff --git a/src/ci.ts b/src/ci.ts
index 8d0d80b..fd8f4dc 100644
--- a/src/ci.ts
+++ b/src/ci.ts
@@ -9,17 +9,19 @@ import fs from "./fs"
 import yargs from "yargs"
 import async from "async"
 import * as config from "./apm"
-import Command from "./command"
+import Command, { LogCommandResultsArgs } from "./command"
+import type { CliOptions, RunCallback } from "./apm-cli"
 
 export default class Ci extends Command {
+  private atomDirectory = config.getAtomDirectory()
+  private atomNpmPath = require.resolve("npm/bin/npm-cli")
+  private atomNodeDirectory: string
   constructor() {
     super()
-    this.atomDirectory = config.getAtomDirectory()
     this.atomNodeDirectory = path.join(this.atomDirectory, ".node-gyp")
-    this.atomNpmPath = require.resolve("npm/bin/npm-cli")
   }
 
-  parseOptions(argv) {
+  parseOptions(argv: string[]) {
     const options = yargs(argv).wrap(Math.min(100, yargs.terminalWidth()))
     options.usage(`\
 Usage: apm ci
@@ -63,12 +65,12 @@ but cannot be used to install new packages or dependencies.\
 
     const installOptions = { env, streaming: options.argv.verbose }
 
-    return this.fork(this.atomNpmPath, installArgs, installOptions, (...args) => {
-      return this.logCommandResults(callback, ...Array.from(args))
+    return this.fork(this.atomNpmPath, installArgs, installOptions, (...args: LogCommandResultsArgs) => {
+      return this.logCommandResults(callback, ...args)
     })
   }
 
-  run(options, callback) {
+  run(options: CliOptions, callback: RunCallback) {
     const opts = this.parseOptions(options.commandArgs)
 
     const commands = []
diff --git a/src/clean.ts b/src/clean.ts
index 42dd84f..fd3209d 100644
--- a/src/clean.ts
+++ b/src/clean.ts
@@ -5,15 +5,13 @@
  * Full docs: https://github.com/decaffeinate/decaffeinate/blob/master/docs/suggestions.md
  */
 import yargs from "yargs"
-import Command from "./command"
+import Command, { LogCommandResultsArgs } from "./command"
+import type { CliOptions, RunCallback } from "./apm-cli"
 
 export default class Clean extends Command {
-  constructor() {
-    super()
-    this.atomNpmPath = require.resolve("npm/bin/npm-cli")
-  }
+  private atomNpmPath = require.resolve("npm/bin/npm-cli")
 
-  parseOptions(argv) {
+  parseOptions(argv: string[]) {
     const options = yargs(argv).wrap(Math.min(100, yargs.terminalWidth()))
 
     options.usage(`\
@@ -25,10 +23,10 @@ as a dependency in the package.json file.\
     return options.alias("h", "help").describe("help", "Print this usage message")
   }
 
-  run(options, callback) {
+  run(options: CliOptions, callback: RunCallback) {
     process.stdout.write("Removing extraneous modules ")
-    return this.fork(this.atomNpmPath, ["prune"], (...args) => {
-      return this.logCommandResults(callback, ...Array.from(args))
+    return this.fork(this.atomNpmPath, ["prune"], (...args: LogCommandResultsArgs) => {
+      return this.logCommandResults(callback, ...args)
     })
   }
 }
diff --git a/src/command.ts b/src/command.ts
index eeb82b6..2000a02 100644
--- a/src/command.ts
+++ b/src/command.ts
@@ -13,7 +13,13 @@ import semver from "semver"
 import * as config from "./apm"
 import * as git from "./git"
 
+export type LogCommandResultsArgs = [code: number, stderr?: string, stdout?: string]
+
 export default class Command {
+  protected electronVersion: string
+  installedAtomVersion: string
+  protected resourcePath: string
+  npm: typeof import("npm")
   constructor() {
     this.logCommandResults = this.logCommandResults.bind(this)
     this.logCommandResultsIfFail = this.logCommandResultsIfFail.bind(this)
@@ -89,7 +95,7 @@ export default class Command {
     }
   }
 
-  logCommandResults(callback, code, stderr = "", stdout = "") {
+  logCommandResults(callback: (error?: string) => void, code: number, stderr = "", stdout = "") {
     if (code === 0) {
       this.logSuccess()
       return callback()
@@ -99,7 +105,7 @@ export default class Command {
     }
   }
 
-  logCommandResultsIfFail(callback, code, stderr = "", stdout = "") {
+  logCommandResultsIfFail(callback: (error?: string) => void, code: number, stderr = "", stdout = "") {
     if (code === 0) {
       return callback()
     } else {
@@ -108,7 +114,7 @@ export default class Command {
     }
   }
 
-  normalizeVersion(version) {
+  normalizeVersion(version: string) {
     if (typeof version === "string") {
       // Remove commit SHA suffix
       return version.replace(/-.*$/, "")
@@ -119,11 +125,15 @@ export default class Command {
 
   loadInstalledAtomMetadata(callback) {
     return this.getResourcePath((resourcePath) => {
-      let electronVersion
+      let electronVersion: string | undefined
       try {
-        let left, version
-        ;({ version, electronVersion } = (left = require(path.join(resourcePath, "package.json"))) != null ? left : {})
-        version = this.normalizeVersion(version)
+        const resourcePathJson: { version: string; electronVersion: string } & Record<string, any> =
+          require(path.join(resourcePath, "package.json")) ?? {}
+
+        electronVersion = resourcePath.electronVersion
+
+        const version = this.normalizeVersion(resourcePathJson.version)
+
         if (semver.valid(version)) {
           this.installedAtomVersion = version
         }
diff --git a/src/config.ts b/src/config.ts
index 3308bf1..7a80154 100644
--- a/src/config.ts
+++ b/src/config.ts
@@ -7,16 +7,18 @@ import path from "path"
 import yargs from "yargs"
 import * as apm from "./apm"
 import Command from "./command"
+import type { CliOptions, RunCallback } from "./apm-cli"
 
 export default class Config extends Command {
+  private atomDirectory = apm.getAtomDirectory()
+  private atomNpmPath = require.resolve("npm/bin/npm-cli")
+  private atomNodeDirectory: string
   constructor() {
     super()
-    const atomDirectory = apm.getAtomDirectory()
-    this.atomNodeDirectory = path.join(atomDirectory, ".node-gyp")
-    this.atomNpmPath = require.resolve("npm/bin/npm-cli")
+    this.atomNodeDirectory = path.join(this.atomDirectory, ".node-gyp")
   }
 
-  parseOptions(argv) {
+  parseOptions(argv: string[]) {
     const options = yargs(argv).wrap(Math.min(100, yargs.terminalWidth()))
     options.usage(`\
 
@@ -30,7 +32,7 @@ Usage: apm config set <key> <value>
     return options.alias("h", "help").describe("help", "Print this usage message")
   }
 
-  run(options, callback) {
+  run(options: CliOptions, callback: RunCallback) {
     options = this.parseOptions(options.commandArgs)
 
     let configArgs = ["--globalconfig", apm.getGlobalConfigPath(), "--userconfig", apm.getUserConfigPath(), "config"]
diff --git a/src/dedupe.ts b/src/dedupe.ts
index 2f3ea23..b49df5e 100644
--- a/src/dedupe.ts
+++ b/src/dedupe.ts
@@ -8,19 +8,22 @@ import path from "path"
 import async from "async"
 import yargs from "yargs"
 import * as config from "./apm"
-import Command from "./command"
+import Command, { LogCommandResultsArgs } from "./command"
 import fs from "./fs"
+import type { CliOptions, RunCallback } from "./apm-cli"
 
 export default class Dedupe extends Command {
+  private atomDirectory = config.getAtomDirectory()
+  private atomNpmPath = require.resolve("npm/bin/npm-cli")
+  atomPackagesDirectory: string
+  private atomNodeDirectory: string
   constructor() {
     super()
-    this.atomDirectory = config.getAtomDirectory()
     this.atomPackagesDirectory = path.join(this.atomDirectory, "packages")
     this.atomNodeDirectory = path.join(this.atomDirectory, ".node-gyp")
-    this.atomNpmPath = require.resolve("npm/bin/npm-cli")
   }
 
-  parseOptions(argv) {
+  parseOptions(argv: string[]) {
     const options = yargs(argv).wrap(Math.min(100, yargs.terminalWidth()))
     options.usage(`\
 
@@ -36,8 +39,8 @@ This command is experimental.\
   dedupeModules(options, callback) {
     process.stdout.write("Deduping modules ")
 
-    return this.forkDedupeCommand(options, (...args) => {
-      return this.logCommandResults(callback, ...Array.from(args))
+    return this.forkDedupeCommand(options, (...args: LogCommandResultsArgs) => {
+      return this.logCommandResults(callback, ...args)
     })
   }
 
@@ -79,7 +82,7 @@ This command is experimental.\
     return fs.makeTreeSync(this.atomNodeDirectory)
   }
 
-  run(options, callback) {
+  run(options: CliOptions, callback: RunCallback) {
     const { cwd } = options
     options = this.parseOptions(options.commandArgs)
     options.cwd = cwd
diff --git a/src/deprecated-packages.ts b/src/deprecated-packages.ts
index f9aa20a..344b321 100644
--- a/src/deprecated-packages.ts
+++ b/src/deprecated-packages.ts
@@ -1,19 +1,22 @@
-/*
- * decaffeinate suggestions:
- * DS102: Remove unnecessary code created because of implicit returns
- * DS104: Avoid inline assignments
- * DS207: Consider shorter variations of null checks
- * Full docs: https://github.com/decaffeinate/decaffeinate/blob/master/docs/suggestions.md
- */
 import semver from "semver"
-let deprecatedPackages = null
+let deprecatedPackages: DeprecatedPackages | undefined
 
-export function isDeprecatedPackage(name, version) {
-  if (deprecatedPackages == null) {
-    let left
-    deprecatedPackages = (left = require("../deprecated-packages")) != null ? left : {}
+type DeprecatedPackage = {
+  version?: string
+  hasDeprecations?: boolean
+  latestHasDeprecations?: boolean
+  message?: string
+  hasAlternative?: boolean
+  alternative?: string
+}
+
+type DeprecatedPackages = Record<string, DeprecatedPackage>
+
+export function isDeprecatedPackage(name: string, version: string) {
+  if (deprecatedPackages === undefined) {
+    deprecatedPackages = require("../deprecated-packages") as DeprecatedPackages
   }
-  if (!deprecatedPackages.hasOwnProperty(name)) {
+  if (!(name in deprecatedPackages)) {
     return false
   }
 
diff --git a/src/develop.ts b/src/develop.ts
index e5650ec..cd75fc4 100644
--- a/src/develop.ts
+++ b/src/develop.ts
@@ -11,20 +11,23 @@ import path from "path"
 import async from "async"
 import yargs from "yargs"
 import * as config from "./apm"
-import Command from "./command"
+import Command, { LogCommandResultsArgs } from "./command"
 import Install from "./install"
 import * as git from "./git"
 import Link from "./link"
 import * as request from "./request"
+import { PackageMetadata, unkownPackage } from "./packages"
+import type { CliOptions, RunCallback } from "./apm-cli"
 
 export default class Develop extends Command {
+  private atomDirectory = config.getAtomDirectory()
+  atomDevPackagesDirectory: string
   constructor() {
     super()
-    this.atomDirectory = config.getAtomDirectory()
     this.atomDevPackagesDirectory = path.join(this.atomDirectory, "dev", "packages")
   }
 
-  parseOptions(argv) {
+  parseOptions(argv: string[]) {
     const options = yargs(argv).wrap(Math.min(100, yargs.terminalWidth()))
 
     options.usage(`\
@@ -44,17 +47,17 @@ cmd-shift-o to run the package out of the newly cloned repository.\
     return options.alias("h", "help").describe("help", "Print this usage message")
   }
 
-  getRepositoryUrl(packageName, callback) {
+  getRepositoryUrl(packageName: string, callback) {
     const requestSettings = {
       url: `${config.getAtomPackagesUrl()}/${packageName}`,
       json: true,
     }
-    return request.get(requestSettings, function (error, response, body = {}) {
+    return request.get(requestSettings, function (error, response, body: PackageMetadata = unkownPackage) {
       if (error != null) {
         return callback(`Request for package information failed: ${error.message}`)
       } else if (response.statusCode === 200) {
-        let repositoryUrl
-        if ((repositoryUrl = body.repository.url)) {
+        const repositoryUrl = body.repository?.url
+        if (repositoryUrl) {
           return callback(null, repositoryUrl)
         } else {
           return callback(`No repository URL found for package: ${packageName}`)
@@ -66,7 +69,7 @@ cmd-shift-o to run the package out of the newly cloned repository.\
     })
   }
 
-  cloneRepository(repoUrl, packageDirectory, options, callback = function () {}) {
+  cloneRepository(repoUrl: string, packageDirectory: string, options, callback = function () {}) {
     return config.getSetting("git", (command) => {
       if (command == null) {
         command = "git"
@@ -76,30 +79,30 @@ cmd-shift-o to run the package out of the newly cloned repository.\
         process.stdout.write(`Cloning ${repoUrl} `)
       }
       git.addGitToEnv(process.env)
-      return this.spawn(command, args, (...args) => {
+      return this.spawn(command, args, (...logargs: LogCommandResultsArgs) => {
         if (options.argv.json) {
-          return this.logCommandResultsIfFail(callback, ...Array.from(args))
+          return this.logCommandResultsIfFail(callback, ...logargs)
         } else {
-          return this.logCommandResults(callback, ...Array.from(args))
+          return this.logCommandResults(callback, ...logargs)
         }
       })
     })
   }
 
-  installDependencies(packageDirectory, options, callback = function () {}) {
+  installDependencies(packageDirectory: string, options, callback = function () {}) {
     process.chdir(packageDirectory)
     const installOptions = { ...options }
 
     return new Install().run(installOptions, callback)
   }
 
-  linkPackage(packageDirectory, options, callback = function () {}) {
+  linkPackage(packageDirectory: string, options, callback = function () {}) {
     const linkOptions = { ...options }
     linkOptions.commandArgs = [packageDirectory, "--dev"]
     return new Link().run(linkOptions, callback)
   }
 
-  run(options, callback) {
+  run(options: CliOptions, callback: RunCallback) {
     let left
     const packageName = options.commandArgs.shift()
 
diff --git a/src/disable.ts b/src/disable.ts
index 447c909..4afffd8 100644
--- a/src/disable.ts
+++ b/src/disable.ts
@@ -12,9 +12,10 @@ import yargs from "yargs"
 import * as config from "./apm"
 import Command from "./command"
 import List from "./list"
+import type { CliOptions, RunCallback } from "./apm-cli"
 
 export default class Disable extends Command {
-  parseOptions(argv) {
+  parseOptions(argv: string[]) {
     const options = yargs(argv).wrap(Math.min(100, yargs.terminalWidth()))
     options.usage(`\
 
@@ -43,7 +44,7 @@ Disables the named package(s).\
     )
   }
 
-  run(options, callback) {
+  run(options: CliOptions, callback: RunCallback) {
     let settings
     options = this.parseOptions(options.commandArgs)
 
diff --git a/src/docs.ts b/src/docs.ts
index fe32e10..80806ea 100644
--- a/src/docs.ts
+++ b/src/docs.ts
@@ -8,9 +8,10 @@
 import yargs from "yargs"
 import open from "open"
 import View from "./view"
+import type { CliOptions, RunCallback } from "./apm-cli"
 
 export default class Docs extends View {
-  parseOptions(argv) {
+  parseOptions(argv: string[]) {
     const options = yargs(argv).wrap(Math.min(100, yargs.terminalWidth()))
     options.usage(`\
 
@@ -26,7 +27,7 @@ Open a package's homepage in the default browser.\
     return open(repositoryUrl)
   }
 
-  run(options, callback) {
+  run(options: CliOptions, callback: RunCallback) {
     options = this.parseOptions(options.commandArgs)
     const [packageName] = Array.from(options.argv._)
 
diff --git a/src/enable.ts b/src/enable.ts
index 81530d1..8acbb7c 100644
--- a/src/enable.ts
+++ b/src/enable.ts
@@ -11,9 +11,10 @@ import CSON from "season"
 import yargs from "yargs"
 import * as config from "./apm"
 import Command from "./command"
+import type { CliOptions, RunCallback } from "./apm-cli"
 
 export default class Enable extends Command {
-  parseOptions(argv) {
+  parseOptions(argv: string[]) {
     const options = yargs(argv).wrap(Math.min(100, yargs.terminalWidth()))
     options.usage(`\
 
@@ -24,7 +25,7 @@ Enables the named package(s).\
     return options.alias("h", "help").describe("help", "Print this usage message")
   }
 
-  run(options, callback) {
+  run(options: CliOptions, callback: RunCallback) {
     let error, left, settings
     options = this.parseOptions(options.commandArgs)
     let packageNames = this.packageNamesFromArgv(options.argv)
diff --git a/src/featured.ts b/src/featured.ts
index 281d7a1..637cacc 100644
--- a/src/featured.ts
+++ b/src/featured.ts
@@ -11,9 +11,10 @@ import Command from "./command"
 import * as config from "./apm"
 import * as request from "./request"
 import { tree } from "./tree"
+import type { CliOptions, RunCallback } from "./apm-cli"
 
 export default class Featured extends Command {
-  parseOptions(argv) {
+  parseOptions(argv: string[]) {
     const options = yargs(argv).wrap(Math.min(100, yargs.terminalWidth()))
     options.usage(`\
 
@@ -81,7 +82,7 @@ atom.io registry.\
     })
   }
 
-  run(options, callback) {
+  run(options: CliOptions, callback: RunCallback) {
     options = this.parseOptions(options.commandArgs)
 
     const listCallback = function (error, packages) {
diff --git a/src/fs.ts b/src/fs.ts
index b481705..477e231 100644
--- a/src/fs.ts
+++ b/src/fs.ts
@@ -49,7 +49,9 @@ const fsAdditions = {
   },
 }
 
-export default new Proxy(
+type ProxyFS = typeof import("fs-plus") & typeof fsAdditions
+
+export default new Proxy<ProxyFS>(
   {},
   {
     get(target, key) {
diff --git a/src/init.ts b/src/init.ts
index c73297f..3511345 100644
--- a/src/init.ts
+++ b/src/init.ts
@@ -9,11 +9,12 @@ import path from "path"
 import yargs from "yargs"
 import Command from "./command"
 import fs from "./fs"
+import type { CliOptions, RunCallback } from "./apm-cli"
 
 const supportedSyntaxes = ["coffeescript", "javascript"]
 
 export default class Init extends Command {
-  parseOptions(argv) {
+  parseOptions(argv: string[]) {
     const options = yargs(argv).wrap(Math.min(100, yargs.terminalWidth()))
 
     options.usage(`\
@@ -49,7 +50,7 @@ on the option selected.\
     return options.string("template").describe("template", "Path to the package or theme template")
   }
 
-  run(options, callback) {
+  run(options: CliOptions, callback: RunCallback) {
     let templatePath
     options = this.parseOptions(options.commandArgs)
     if (options.argv.package?.length > 0) {
diff --git a/src/install.ts b/src/install.ts
index d5d0771..ef4722e 100644
--- a/src/install.ts
+++ b/src/install.ts
@@ -22,18 +22,23 @@ import fs from "./fs"
 import RebuildModuleCache from "./rebuild-module-cache"
 import * as request from "./request"
 import { isDeprecatedPackage } from "./deprecated-packages"
+import type { CliOptions, RunCallback } from "./apm-cli"
 
 export default class Install extends Command {
+  private atomDirectory = config.getAtomDirectory()
+  private atomPackagesDirectory: string
+  private atomNodeDirectory: string
+  private atomNpmPath = require.resolve("npm/bin/npm-cli")
+  private repoLocalPackagePathRegex = /^file:(?!\/\/)(.*)/
+  verbose: boolean
+
   constructor() {
     super()
-    this.atomDirectory = config.getAtomDirectory()
     this.atomPackagesDirectory = path.join(this.atomDirectory, "packages")
     this.atomNodeDirectory = path.join(this.atomDirectory, ".node-gyp")
-    this.atomNpmPath = require.resolve("npm/bin/npm-cli")
-    this.repoLocalPackagePathRegex = /^file:(?!\/\/)(.*)/
   }
 
-  parseOptions(argv) {
+  parseOptions(argv: string[]) {
     const options = yargs(argv).wrap(Math.min(100, yargs.terminalWidth()))
     options.usage(`\
 
@@ -749,7 +754,7 @@ Run apm -v after installing Git to see what version has been detected.\
     }
   }
 
-  run(options, callback) {
+  run(options: CliOptions, callback: RunCallback) {
     let packageNames
     options = this.parseOptions(options.commandArgs)
     const packagesFilePath = options.argv["packages-file"]
diff --git a/src/link.ts b/src/link.ts
index 3f251a5..b25395c 100644
--- a/src/link.ts
+++ b/src/link.ts
@@ -11,9 +11,10 @@ import yargs from "yargs"
 import Command from "./command"
 import * as config from "./apm"
 import fs from "./fs"
+import type { CliOptions, RunCallback } from "./apm-cli"
 
 export default class Link extends Command {
-  parseOptions(argv) {
+  parseOptions(argv: string[]) {
     const options = yargs(argv).wrap(Math.min(100, yargs.terminalWidth()))
     options.usage(`\
 
@@ -28,7 +29,7 @@ Run \`apm links\` to view all the currently linked packages.\
     return options.alias("d", "dev").boolean("dev").describe("dev", "Link to ~/.atom/dev/packages")
   }
 
-  run(options, callback) {
+  run(options: CliOptions, callback: RunCallback) {
     let left, targetPath
     options = this.parseOptions(options.commandArgs)
 
diff --git a/src/links.ts b/src/links.ts
index c36d3cb..1cfd8cf 100644
--- a/src/links.ts
+++ b/src/links.ts
@@ -9,15 +9,13 @@ import Command from "./command"
 import * as config from "./apm"
 import fs from "./fs"
 import { tree } from "./tree"
+import type { CliOptions, RunCallback } from "./apm-cli"
 
 export default class Links extends Command {
-  constructor() {
-    super()
-    this.devPackagesPath = path.join(config.getAtomDirectory(), "dev", "packages")
-    this.packagesPath = path.join(config.getAtomDirectory(), "packages")
-  }
+  private devPackagesPath = path.join(config.getAtomDirectory(), "dev", "packages")
+  private packagesPath = path.join(config.getAtomDirectory(), "packages")
 
-  parseOptions(argv) {
+  parseOptions(argv: string[]) {
     const options = yargs(argv).wrap(Math.min(100, yargs.terminalWidth()))
     options.usage(`\
 
@@ -62,7 +60,7 @@ List all of the symlinked atom packages in ~/.atom/packages and
     })
   }
 
-  run(options, callback) {
+  run(options: CliOptions, callback: RunCallback) {
     this.logLinks(this.devPackagesPath)
     this.logLinks(this.packagesPath)
     return callback()
diff --git a/src/list.ts b/src/list.ts
index 7432313..5c534e6 100644
--- a/src/list.ts
+++ b/src/list.ts
@@ -13,13 +13,16 @@ import fs from "./fs"
 import * as config from "./apm"
 import { tree } from "./tree"
 import { getRepository } from "./packages"
+import type { CliOptions, RunCallback } from "./apm-cli"
 
 export default class List extends Command {
+  private userPackagesDirectory = path.join(config.getAtomDirectory(), "packages")
+  private devPackagesDirectory = path.join(config.getAtomDirectory(), "dev", "packages")
+  private disabledPackages?: string[]
   constructor() {
     super()
-    let configPath
-    this.userPackagesDirectory = path.join(config.getAtomDirectory(), "packages")
-    this.devPackagesDirectory = path.join(config.getAtomDirectory(), "dev", "packages")
+    let configPath: string
+
     if ((configPath = CSON.resolve(path.join(config.getAtomDirectory(), "config")))) {
       try {
         this.disabledPackages = CSON.readFileSync(configPath)?.["*"]?.core?.disabledPackages
@@ -32,7 +35,7 @@ export default class List extends Command {
     }
   }
 
-  parseOptions(argv) {
+  parseOptions(argv: string[]) {
     const options = yargs(argv).wrap(Math.min(100, yargs.terminalWidth()))
     options.usage(`\
 
@@ -284,7 +287,7 @@ List all the installed packages and also the packages bundled with Atom.\
     })
   }
 
-  run(options, callback) {
+  run(options: CliOptions, callback: RunCallback) {
     options = this.parseOptions(options.commandArgs)
 
     if (options.argv.json) {
diff --git a/src/login.ts b/src/login.ts
index 00f09a6..7d61ce8 100644
--- a/src/login.ts
+++ b/src/login.ts
@@ -12,13 +12,14 @@ import open from "open"
 
 import * as auth from "./auth"
 import Command from "./command"
+import type { CliOptions, RunCallback } from "./apm-cli"
 
 export default class Login extends Command {
-  constructor(...args) {
+  constructor() {
+    super()
     this.welcomeMessage = this.welcomeMessage.bind(this)
     this.getToken = this.getToken.bind(this)
     this.saveToken = this.saveToken.bind(this)
-    super(...args)
   }
 
   static getTokenOrLogin(callback) {
@@ -31,7 +32,7 @@ export default class Login extends Command {
     })
   }
 
-  parseOptions(argv) {
+  parseOptions(argv: string[]) {
     const options = yargs(argv).wrap(Math.min(100, yargs.terminalWidth()))
 
     options.usage(`\
@@ -44,7 +45,7 @@ be used to identify you when publishing packages to atom.io.\
     return options.string("token").describe("token", "atom.io API token")
   }
 
-  run(options, callback) {
+  run(options: CliOptions, callback: RunCallback) {
     options = this.parseOptions(options.commandArgs)
     return Q({ token: options.argv.token })
       .then(this.welcomeMessage)
diff --git a/src/package-converter.ts b/src/package-converter.ts
index f413834..d4bc3c5 100644
--- a/src/package-converter.ts
+++ b/src/package-converter.ts
@@ -20,7 +20,11 @@ import * as request from "./request"
 
 // Convert a TextMate bundle to an Atom package
 export default class PackageConverter {
-  constructor(sourcePath, destinationPath) {
+  sourcePath: string
+  destinationPath: string
+  plistExtensions: string[]
+  directoryMappings: { Preferences: string; Snippets: string; Syntaxes: string }
+  constructor(sourcePath: string, destinationPath: string) {
     this.sourcePath = sourcePath
     this.destinationPath = path.resolve(destinationPath)
 
@@ -33,7 +37,7 @@ export default class PackageConverter {
     }
   }
 
-  convert(callback) {
+  convert(callback: Function) {
     const { protocol } = url.parse(this.sourcePath)
     if (protocol === "http:" || protocol === "https:") {
       return this.downloadBundle(callback)
@@ -48,7 +52,7 @@ export default class PackageConverter {
     return (downloadUrl += "/archive/master.tar.gz")
   }
 
-  downloadBundle(callback) {
+  downloadBundle(callback: Function) {
     const tempPath = temp.mkdirSync("atom-bundle-")
     const requestOptions = { url: this.getDownloadUrl() }
     return request.createReadStream(requestOptions, (readStream) => {
@@ -69,8 +73,8 @@ export default class PackageConverter {
     })
   }
 
-  copyDirectories(sourcePath, callback) {
-    let packageName
+  copyDirectories(sourcePath: string, callback: Function) {
+    let packageName: string
     sourcePath = path.resolve(sourcePath)
     try {
       packageName = JSON.parse(fs.readFileSync(path.join(sourcePath, "package.json")))?.packageName
@@ -92,7 +96,13 @@ export default class PackageConverter {
     return delete object.keyEquivalent
   }
 
-  convertSettings(settings) {
+  convertSettings(settings: {
+    shellVariables: { name: any; value: any }[] | {}
+    increaseIndentPattern: any
+    decreaseIndentPattern: any
+    foldingStopMarker: any
+    completions: any
+  }) {
     if (settings.shellVariables) {
       const shellVariables = {}
       for (const { name, value } of settings.shellVariables) {
@@ -114,7 +124,7 @@ export default class PackageConverter {
     }
   }
 
-  readFileSync(filePath) {
+  readFileSync(filePath: string) {
     if (this.plistExtensions.includes(path.extname(filePath))) {
       return plist.parseFileSync(filePath)
     } else if ([".json", ".cson"].includes(path.extname(filePath))) {
@@ -122,15 +132,15 @@ export default class PackageConverter {
     }
   }
 
-  writeFileSync(filePath, object = {}) {
+  writeFileSync(filePath: string, object = {}) {
     this.filterObject(object)
     if (Object.keys(object).length > 0) {
       return CSON.writeFileSync(filePath, object)
     }
   }
 
-  convertFile(sourcePath, destinationDir) {
-    let contents
+  convertFile(sourcePath: string, destinationDir: string) {
+    let contents: {}
     const extension = path.extname(sourcePath)
     let destinationName = `${path.basename(sourcePath, extension)}.cson`
     destinationName = destinationName.toLowerCase()
@@ -145,7 +155,7 @@ export default class PackageConverter {
     return this.writeFileSync(destinationPath, contents)
   }
 
-  normalizeFilenames(directoryPath) {
+  normalizeFilenames(directoryPath: string) {
     if (!fs.isDirectorySync(directoryPath)) {
       return
     }
@@ -176,7 +186,7 @@ export default class PackageConverter {
     })()
   }
 
-  convertSnippets(packageName, source) {
+  convertSnippets(packageName: string, source: string) {
     let sourceSnippets = path.join(source, "snippets")
     if (!fs.isDirectorySync(sourceSnippets)) {
       sourceSnippets = path.join(source, "Snippets")
@@ -233,7 +243,7 @@ export default class PackageConverter {
     return this.normalizeFilenames(destination)
   }
 
-  convertPreferences(packageName, source) {
+  convertPreferences(packageName: string, source: string) {
     let sourcePreferences = path.join(source, "preferences")
     if (!fs.isDirectorySync(sourcePreferences)) {
       sourcePreferences = path.join(source, "Preferences")
@@ -245,14 +255,14 @@ export default class PackageConverter {
     const preferencesBySelector = {}
     const destination = path.join(this.destinationPath, "settings")
     for (const child of fs.readdirSync(sourcePreferences)) {
-      let left, properties
+      let left, properties: { [x: string]: any; editor?: any }
       const { scope, settings } = (left = this.readFileSync(path.join(sourcePreferences, child))) != null ? left : {}
       if (!scope || !settings) {
         continue
       }
 
       if ((properties = this.convertSettings(settings))) {
-        let selector
+        let selector: string
         try {
           selector = new ScopeSelector(scope).toCssSelector()
         } catch (e) {
@@ -277,7 +287,7 @@ export default class PackageConverter {
     return this.normalizeFilenames(destination)
   }
 
-  convertGrammars(source) {
+  convertGrammars(source: string) {
     let sourceSyntaxes = path.join(source, "syntaxes")
     if (!fs.isDirectorySync(sourceSyntaxes)) {
       sourceSyntaxes = path.join(source, "Syntaxes")
diff --git a/src/packages.ts b/src/packages.ts
index fc96e5c..43a7c79 100644
--- a/src/packages.ts
+++ b/src/packages.ts
@@ -6,6 +6,10 @@
  * Full docs: https://github.com/decaffeinate/decaffeinate/blob/master/docs/suggestions.md
  */
 import url from "url"
+import { PackageMetadata } from "atom/src/package-manager"
+export { PackageMetadata } from "atom/src/package-manager"
+
+export const unkownPackage = { name: "unkown", version: "0.0.0" }
 
 // Package helpers
 // Parse the repository in `name/owner` format from the package metadata.
@@ -13,9 +17,9 @@ import url from "url"
 // pack - The package metadata object.
 //
 // Returns a name/owner string or null if not parseable.
-export function getRepository(pack = {}) {
-  let repository
-  if ((repository = pack.repository?.url != null ? pack.repository?.url : pack.repository)) {
+export function getRepository(pack: PackageMetadata = unkownPackage) {
+  const repository = getUrl(pack)
+  if (repository) {
     const repoPath = url.parse(repository.replace(/\.git$/, "")).pathname
     const [name, owner] = Array.from(repoPath.split("/").slice(-2))
     if (name && owner) {
@@ -25,10 +29,15 @@ export function getRepository(pack = {}) {
   return null
 }
 
-// Determine remote from package metadata.
+// Determine remote from package metadata (url)
 //
 // pack - The package metadata object.
 // Returns a the remote or 'origin' if not parseable.
-export function getRemote(pack = {}) {
-  return pack.repository?.url || pack.repository || "origin"
+export function getRemote(pack: PackageMetadata = unkownPackage) {
+  return getUrl(pack) || "origin"
+}
+
+/** Get the repository */
+function getUrl(pack: PackageMetadata = unkownPackage) {
+  return typeof pack.repository === "object" && "url" in pack.repository ? pack.repository.url : pack.repository
 }
diff --git a/src/publish.ts b/src/publish.ts
index 2bab3f5..1b19d5d 100644
--- a/src/publish.ts
+++ b/src/publish.ts
@@ -12,19 +12,16 @@ import Git from "git-utils"
 import semver from "semver"
 import fs from "./fs"
 import * as config from "./apm"
-import Command from "./command"
+import Command, { LogCommandResultsArgs } from "./command"
 import Login from "./login"
 import * as Packages from "./packages"
 import * as request from "./request"
 
 export default class Publish extends Command {
-  constructor() {
-    super()
-    this.userConfigPath = config.getUserConfigPath()
-    this.atomNpmPath = require.resolve("npm/bin/npm-cli")
-  }
+  userConfigPath = config.getUserConfigPath()
+  atomNpmPath = require.resolve("npm/bin/npm-cli")
 
-  parseOptions(argv) {
+  parseOptions(argv: string[]) {
     const options = yargs(argv).wrap(Math.min(100, yargs.terminalWidth()))
     options.usage(`\
 
@@ -59,7 +56,7 @@ have published it.\
   // version  - The new version or version increment.
   // callback - The callback function to invoke with an error as the first
   //            argument and a the generated tag string as the second argument.
-  versionPackage(version, callback) {
+  versionPackage(version: string, callback) {
     process.stdout.write("Preparing and tagging a new version ")
     const versionArgs = ["version", version, "-m", "Prepare v%s release"]
     return this.fork(this.atomNpmPath, versionArgs, (code, stderr = "", stdout = "") => {
@@ -79,11 +76,11 @@ have published it.\
   //  pack - The package metadata.
   //  callback - The callback function to invoke with an error as the first
   //             argument.
-  pushVersion(tag, pack, callback) {
+  pushVersion(tag: string, pack: Packages.PackageMetadata, callback: Function) {
     process.stdout.write(`Pushing ${tag} tag `)
     const pushArgs = ["push", Packages.getRemote(pack), "HEAD", tag]
-    return this.spawn("git", pushArgs, (...args) => {
-      return this.logCommandResults(callback, ...Array.from(args))
+    return this.spawn("git", pushArgs, (...args: LogCommandResultsArgs) => {
+      return this.logCommandResults(callback, ...args)
     })
   }
 
@@ -97,7 +94,7 @@ have published it.\
   // callback - The callback function to invoke when either the tag is available
   //            or the maximum numbers of requests for the tag have been made.
   //            No arguments are passed to the callback when it is invoked.
-  waitForTagToBeAvailable(pack, tag, callback) {
+  waitForTagToBeAvailable(pack: Packages.PackageMetadata, tag: string, callback: Function) {
     let retryCount = 5
     const interval = 1000
     const requestSettings = {
@@ -129,7 +126,7 @@ have published it.\
   // packageName - The string package name to check.
   // callback    - The callback function invoke with an error as the first
   //               argument and true/false as the second argument.
-  packageExists(packageName, callback) {
+  packageExists(packageName: string, callback: Function) {
     return Login.getTokenOrLogin(function (error, token) {
       if (error != null) {
         return callback(error)
@@ -156,7 +153,7 @@ have published it.\
   //
   // pack - The package metadata.
   // callback - The callback function.
-  registerPackage(pack, callback) {
+  registerPackage(pack: Packages.PackageMetadata, callback: Function) {
     if (!pack.name) {
       callback("Required name field in package.json not found")
       return
@@ -216,7 +213,7 @@ have published it.\
   // tag - The string Git tag of the new version.
   // callback - The callback function to invoke with an error as the first
   //            argument.
-  createPackageVersion(packageName, tag, options, callback) {
+  createPackageVersion(packageName: string, tag: string, options: { rename: boolean }, callback: Function) {
     return Login.getTokenOrLogin(function (error, token) {
       if (error != null) {
         callback(error)
@@ -254,7 +251,7 @@ have published it.\
   // options - An options Object (optional).
   // callback - The callback function to invoke when done with an error as the
   //            first argument.
-  publishPackage(pack, tag, ...remaining) {
+  publishPackage(pack: Packages.PackageMetadata, tag: string, ...remaining) {
     let options
     if (remaining.length >= 2) {
       options = remaining.shift()
@@ -276,7 +273,7 @@ have published it.\
     })
   }
 
-  logFirstTimePublishMessage(pack) {
+  logFirstTimePublishMessage(pack: Packages.PackageMetadata) {
     process.stdout.write("Congrats on publishing a new package!".rainbow)
     // :+1: :package: :tada: when available
     if (process.platform === "darwin") {
@@ -299,7 +296,7 @@ have published it.\
     }
   }
 
-  saveMetadata(pack, callback) {
+  saveMetadata(pack: Packages.PackageMetadata, callback: Function) {
     const metadataPath = path.resolve("package.json")
     const metadataJson = JSON.stringify(pack, null, 2)
     return fs.writeFile(metadataPath, `${metadataJson}\n`, callback)
@@ -338,7 +335,7 @@ have published it.\
   }
 
   // Rename package if necessary
-  renamePackage(pack, name, callback) {
+  renamePackage(pack: Packages.PackageMetadata, name: string, callback: Function) {
     if (name?.length > 0) {
       if (pack.name === name) {
         return callback("The new package name must be different than the name in the package.json file")
@@ -382,12 +379,12 @@ have published it.\
     }
   }
 
-  setPackageName(pack, name, callback) {
+  setPackageName(pack: Packages.PackageMetadata, name: string, callback: Function) {
     pack.name = name
     return this.saveMetadata(pack, callback)
   }
 
-  validateSemverRanges(pack) {
+  validateSemverRanges(pack: Packages.PackageMetadata) {
     let packageName, semverRange
     if (!pack) {
       return
@@ -431,8 +428,8 @@ have published it.\
   }
 
   // Run the publish command with the given options
-  run(options, callback) {
-    let error, pack
+  run(options, callback: Function) {
+    let error, pack: Packages.PackageMetadata
     options = this.parseOptions(options.commandArgs)
     const { tag } = options.argv
     let { rename } = options.argv
diff --git a/src/rebuild-module-cache.ts b/src/rebuild-module-cache.ts
index e7353ef..3e75e81 100644
--- a/src/rebuild-module-cache.ts
+++ b/src/rebuild-module-cache.ts
@@ -10,14 +10,13 @@ import yargs from "yargs"
 import Command from "./command"
 import * as config from "./apm"
 import fs from "./fs"
+import type { CliOptions, RunCallback } from "./apm-cli"
 
 export default class RebuildModuleCache extends Command {
-  constructor() {
-    super()
-    this.atomPackagesDirectory = path.join(config.getAtomDirectory(), "packages")
-  }
+  atomPackagesDirectory = path.join(config.getAtomDirectory(), "packages")
+  moduleCache?: any
 
-  parseOptions(argv) {
+  parseOptions(argv: string[]) {
     const options = yargs(argv).wrap(Math.min(100, yargs.terminalWidth()))
     options.usage(`\
 
@@ -34,7 +33,7 @@ This command skips all linked packages.\
     return options.alias("h", "help").describe("help", "Print this usage message")
   }
 
-  getResourcePath(callback) {
+  getResourcePath(callback: Function) {
     if (this.resourcePath) {
       return process.nextTick(() => callback(this.resourcePath))
     } else {
@@ -45,8 +44,8 @@ This command skips all linked packages.\
     }
   }
 
-  rebuild(packageDirectory, callback) {
-    return this.getResourcePath((resourcePath) => {
+  rebuild(packageDirectory: string, callback: Function) {
+    return this.getResourcePath((resourcePath: string) => {
       try {
         if (this.moduleCache == null) {
           this.moduleCache = require(path.join(resourcePath, "src", "module-cache"))
@@ -60,7 +59,7 @@ This command skips all linked packages.\
     })
   }
 
-  run(options, callback) {
+  run(options: CliOptions, callback: RunCallback) {
     const commands = []
     fs.list(this.atomPackagesDirectory).forEach((packageName) => {
       const packageDirectory = path.join(this.atomPackagesDirectory, packageName)
@@ -71,9 +70,9 @@ This command skips all linked packages.\
         return
       }
 
-      return commands.push((callback) => {
+      return commands.push((callback: Function) => {
         process.stdout.write(`Rebuilding ${packageName} module cache `)
-        return this.rebuild(packageDirectory, (error) => {
+        return this.rebuild(packageDirectory, (error?: Error) => {
           if (error != null) {
             this.logFailure()
           } else {
diff --git a/src/rebuild.ts b/src/rebuild.ts
index 591a343..778bd2f 100644
--- a/src/rebuild.ts
+++ b/src/rebuild.ts
@@ -9,16 +9,19 @@ import yargs from "yargs"
 import * as config from "./apm"
 import Command from "./command"
 import fs from "./fs"
+import type { CliOptions, RunCallback } from "./apm-cli"
 
 export default class Rebuild extends Command {
+  private atomDirectory = config.getAtomDirectory()
+  private atomNpmPath = require.resolve("npm/bin/npm-cli")
+  private atomNodeDirectory: string
+
   constructor() {
     super()
-    this.atomDirectory = config.getAtomDirectory()
     this.atomNodeDirectory = path.join(this.atomDirectory, ".node-gyp")
-    this.atomNpmPath = require.resolve("npm/bin/npm-cli")
   }
 
-  parseOptions(argv) {
+  parseOptions(argv: string[]) {
     const options = yargs(argv).wrap(Math.min(100, yargs.terminalWidth()))
     options.usage(`\
 
@@ -53,7 +56,7 @@ All the modules will be rebuilt if no module names are specified.\
     return this.fork(this.atomNpmPath, rebuildArgs, { env }, callback)
   }
 
-  run(options, callback) {
+  run(options: CliOptions, callback: RunCallback) {
     options = this.parseOptions(options.commandArgs)
 
     return config.loadNpm((error, npm) => {
diff --git a/src/request.ts b/src/request.ts
index a2e25a7..0e393c9 100644
--- a/src/request.ts
+++ b/src/request.ts
@@ -6,10 +6,10 @@
  * Full docs: https://github.com/decaffeinate/decaffeinate/blob/master/docs/suggestions.md
  */
 import npm from "npm"
-import request from "request"
+import request, { Options, RequestCallback } from "request"
 import * as config from "./apm"
 
-function loadNpm(callback) {
+function loadNpm(callback: Parameters<typeof npm["load"]>[1]) {
   const npmOptions = {
     userconfig: config.getUserConfigPath(),
     globalconfig: config.getGlobalConfigPath(),
@@ -17,7 +17,7 @@ function loadNpm(callback) {
   return npm.load(npmOptions, callback)
 }
 
-function configureRequest(requestOptions, callback) {
+function configureRequest(requestOptions: Options, callback: () => void) {
   return loadNpm(function () {
     let left
     if (requestOptions.proxy == null) {
@@ -40,9 +40,9 @@ function configureRequest(requestOptions, callback) {
   })
 }
 
-export function get(requestOptions, callback) {
+export function get(requestOptions: Options & { retries?: number }, callback: RequestCallback) {
   return configureRequest(requestOptions, function () {
-    let retryCount = requestOptions.retries != null ? requestOptions.retries : 0
+    let retryCount = "retries" in requestOptions ? requestOptions.retries : 0
     let requestsMade = 0
     const tryRequest = function () {
       requestsMade++
@@ -63,19 +63,22 @@ export function get(requestOptions, callback) {
   })
 }
 
-export function del(requestOptions, callback) {
+export function del(requestOptions: Options, callback: RequestCallback) {
   return configureRequest(requestOptions, () => request.del(requestOptions, callback))
 }
 
-export function post(requestOptions, callback) {
+export function post(requestOptions: Options, callback: RequestCallback) {
   return configureRequest(requestOptions, () => request.post(requestOptions, callback))
 }
 
-export function createReadStream(requestOptions, callback) {
+export function createReadStream(
+  requestOptions: Options,
+  callback: { (readStream: any): any; (arg0: request.Request): void }
+) {
   return configureRequest(requestOptions, () => callback(request.get(requestOptions)))
 }
 
-export function getErrorMessage(response, body) {
+export function getErrorMessage(response: request.Response, body: {} | { repository?: { url?: string } }) {
   if (response?.statusCode === 503) {
     return "atom.io is temporarily unavailable, please try again later."
   } else {
@@ -84,6 +87,6 @@ export function getErrorMessage(response, body) {
   }
 }
 
-export function debug(debug) {
+export function debug(debug: boolean) {
   return (request.debug = debug)
 }
diff --git a/src/search.ts b/src/search.ts
index 953dc8d..7272b2d 100644
--- a/src/search.ts
+++ b/src/search.ts
@@ -12,9 +12,10 @@ import * as config from "./apm"
 import * as request from "./request"
 import { tree } from "./tree"
 import { isDeprecatedPackage } from "./deprecated-packages"
+import type { CliOptions, RunCallback } from "./apm-cli"
 
 export default class Search extends Command {
-  parseOptions(argv) {
+  parseOptions(argv: string[]) {
     const options = yargs(argv).wrap(Math.min(100, yargs.terminalWidth()))
     options.usage(`\
 
@@ -63,7 +64,7 @@ Search for Atom packages/themes on the atom.io registry.\
     })
   }
 
-  run(options, callback) {
+  run(options: CliOptions, callback: RunCallback) {
     options = this.parseOptions(options.commandArgs)
     const [query] = Array.from(options.argv._)
 
diff --git a/src/star.ts b/src/star.ts
index 4e6e315..b2cfba7 100644
--- a/src/star.ts
+++ b/src/star.ts
@@ -16,9 +16,10 @@ import fs from "./fs"
 import Login from "./login"
 import * as Packages from "./packages"
 import * as request from "./request"
+import type { CliOptions, RunCallback } from "./apm-cli"
 
 export default class Star extends Command {
-  parseOptions(argv) {
+  parseOptions(argv: string[]) {
     const options = yargs(argv).wrap(Math.min(100, yargs.terminalWidth()))
     options.usage(`\
 
@@ -87,7 +88,7 @@ Run \`apm stars\` to see all your starred packages.\
     return _.uniq(installedPackages)
   }
 
-  run(options, callback) {
+  run(options: CliOptions, callback: RunCallback) {
     let packageNames
     options = this.parseOptions(options.commandArgs)
 
diff --git a/src/stars.ts b/src/stars.ts
index 9a19286..c775344 100644
--- a/src/stars.ts
+++ b/src/stars.ts
@@ -12,9 +12,10 @@ import Install from "./install"
 import Login from "./login"
 import * as request from "./request"
 import { tree } from "./tree"
+import type { CliOptions, RunCallback } from "./apm-cli"
 
 export default class Stars extends Command {
-  parseOptions(argv) {
+  parseOptions(argv: string[]) {
     const options = yargs(argv).wrap(Math.min(100, yargs.terminalWidth()))
     options.usage(`\
 
@@ -123,7 +124,7 @@ List or install starred Atom packages and themes.\
     return callback()
   }
 
-  run(options, callback) {
+  run(options: CliOptions, callback: RunCallback) {
     options = this.parseOptions(options.commandArgs)
     const user = options.argv.user?.toString().trim()
 
diff --git a/src/test.ts b/src/test.ts
index b1e5809..a1c7d35 100644
--- a/src/test.ts
+++ b/src/test.ts
@@ -8,9 +8,10 @@ import yargs from "yargs"
 import temp from "temp"
 import Command from "./command"
 import fs from "./fs"
+import type { CliOptions, RunCallback } from "./apm-cli"
 
 export default class Test extends Command {
-  parseOptions(argv) {
+  parseOptions(argv: string[]) {
     const options = yargs(argv).wrap(Math.min(100, yargs.terminalWidth()))
 
     options.usage(`\
@@ -24,7 +25,7 @@ to the current working directory).\
     return options.alias("p", "path").string("path").describe("path", "Path to atom command")
   }
 
-  run(options, callback) {
+  run(options: CliOptions, callback: RunCallback) {
     let atomCommand
     options = this.parseOptions(options.commandArgs)
     const { env } = process
diff --git a/src/text-mate-theme.ts b/src/text-mate-theme.ts
index 58f6e92..fa37dc9 100644
--- a/src/text-mate-theme.ts
+++ b/src/text-mate-theme.ts
@@ -9,7 +9,24 @@
 import plist from "@atom/plist"
 import { ScopeSelector } from "first-mate"
 
+export type RuleSet = {
+  selector: string
+  comment?: string
+  properties: Record<string, string>
+}
+
+export type ScopeSelectorSettings = {
+  "font-weight"?: string
+  "font-style"?: string
+  "text-decoration"?: string
+  color?: string
+  "background-color"?: string
+}
+
 export default class TextMateTheme {
+  contents: string
+  rulesets: RuleSet[]
+  syntaxVariables: string
   constructor(contents) {
     this.contents = contents
     this.rulesets = []
@@ -17,11 +34,8 @@ export default class TextMateTheme {
   }
 
   buildRulesets() {
-    let left, variableSettings
-    let { settings } = (left = plist.parseStringSync(this.contents)) != null ? left : {}
-    if (settings == null) {
-      settings = []
-    }
+    let variableSettings
+    const settings = plist.parseStringSync(this.contents)?.settings ?? []
 
     for (const setting of settings) {
       const { scope, name } = setting.settings
@@ -188,7 +202,7 @@ atom-text-editor.is-focused .line.cursor-line`,
   }
 
   translateScopeSelectorSettings({ foreground, background, fontStyle }) {
-    const properties = {}
+    const properties: ScopeSelectorSettings = {}
 
     if (fontStyle) {
       const fontStyles = fontStyle.split(/\s+/)
diff --git a/src/theme-converter.ts b/src/theme-converter.ts
index 4c8f9d6..ee341e5 100644
--- a/src/theme-converter.ts
+++ b/src/theme-converter.ts
@@ -12,7 +12,9 @@ import TextMateTheme from "./text-mate-theme"
 
 // Convert a TextMate theme to an Atom theme
 export default class ThemeConverter {
-  constructor(sourcePath, destinationPath) {
+  sourcePath: string
+  destinationPath: string
+  constructor(sourcePath: string, destinationPath: string) {
     this.sourcePath = sourcePath
     this.destinationPath = path.resolve(destinationPath)
   }
diff --git a/src/types/atom.d.ts b/src/types/atom.d.ts
new file mode 100644
index 0000000..2d9f26e
--- /dev/null
+++ b/src/types/atom.d.ts
@@ -0,0 +1,37 @@
+declare module "atom/src/package-manager" {
+  import { Package, Emitter } from "atom"
+
+  /** The content of a package.json */
+  export type PackageMetadata = {
+    name: string
+    version: string
+    repository?: string | { url: string }
+    engines?: { atom?: string }
+    dependencies?: { name: string; version: string }[]
+    devDependencies?: { name: string; version: string }[]
+    apmInstallSource?: { sha: string; type: string }
+  }
+
+  export class PackageManager {
+    readonly initialPackagesActivated: boolean
+
+    getAvailablePackageMetadata(): Array<PackageMetadata>
+
+    activate(): Promise<any>
+    deactivatePackages(): Promise<void>
+    deactivatePackage(name: string, suppressSerialization?: boolean): Promise<void>
+    emitter: Emitter
+    loadedPackages: {
+      [packageName: string]: Package
+    }
+    loadPackage(name: string): void
+    loadPackages(): void
+    serializePackage(pkg: Package): void
+    // serviceHub: ServiceHub
+    packageDirPaths: Array<string>
+    triggerActivationHook(hook: string): void
+    triggerDeferredActivationHooks(): void
+    unloadPackage(name: string): void
+    unloadPackages(): void
+  }
+}
diff --git a/src/uninstall.ts b/src/uninstall.ts
index 27384e6..2cc7dde 100644
--- a/src/uninstall.ts
+++ b/src/uninstall.ts
@@ -13,9 +13,10 @@ import Command from "./command"
 import * as config from "./apm"
 import fs from "./fs"
 import * as request from "./request"
+import type { CliOptions, RunCallback } from "./apm-cli"
 
 export default class Uninstall extends Command {
-  parseOptions(argv) {
+  parseOptions(argv: string[]) {
     const options = yargs(argv).wrap(Math.min(100, yargs.terminalWidth()))
     options.usage(`\
 
@@ -58,7 +59,7 @@ Delete the installed package(s) from the ~/.atom/packages directory.\
     })
   }
 
-  run(options, callback) {
+  run(options: CliOptions, callback: RunCallback) {
     options = this.parseOptions(options.commandArgs)
     const packageNames = this.packageNamesFromArgv(options.argv)
 
diff --git a/src/unlink.ts b/src/unlink.ts
index e62ac6c..5d1c2ac 100644
--- a/src/unlink.ts
+++ b/src/unlink.ts
@@ -11,15 +11,13 @@ import yargs from "yargs"
 import Command from "./command"
 import * as config from "./apm"
 import fs from "./fs"
+import type { CliOptions, RunCallback } from "./apm-cli"
 
 export default class Unlink extends Command {
-  constructor() {
-    super()
-    this.devPackagesPath = path.join(config.getAtomDirectory(), "dev", "packages")
-    this.packagesPath = path.join(config.getAtomDirectory(), "packages")
-  }
+  devPackagesPath = path.join(config.getAtomDirectory(), "dev", "packages")
+  packagesPath = path.join(config.getAtomDirectory(), "packages")
 
-  parseOptions(argv) {
+  parseOptions(argv: string[]) {
     const options = yargs(argv).wrap(Math.min(100, yargs.terminalWidth()))
     options.usage(`\
 
@@ -121,7 +119,7 @@ Run \`apm links\` to view all the currently linked packages.\
     }
   }
 
-  run(options, callback) {
+  run(options: CliOptions, callback: RunCallback) {
     options = this.parseOptions(options.commandArgs)
 
     if (options.argv.all) {
diff --git a/src/unpublish.ts b/src/unpublish.ts
index dceb379..c4597e3 100644
--- a/src/unpublish.ts
+++ b/src/unpublish.ts
@@ -15,9 +15,10 @@ import Command from "./command"
 import * as config from "./apm"
 import fs from "./fs"
 import * as request from "./request"
+import type { CliOptions, RunCallback } from "./apm-cli"
 
 export default class Unpublish extends Command {
-  parseOptions(argv) {
+  parseOptions(argv: string[]) {
     const options = yargs(argv).wrap(Math.min(100, yargs.terminalWidth()))
 
     options.usage(`\
@@ -112,7 +113,7 @@ name is specified.\
     })
   }
 
-  run(options, callback) {
+  run(options: CliOptions, callback: RunCallback) {
     let version
     options = this.parseOptions(options.commandArgs)
     let [name] = Array.from(options.argv._)
diff --git a/src/unstar.ts b/src/unstar.ts
index 7493714..4b1f8af 100644
--- a/src/unstar.ts
+++ b/src/unstar.ts
@@ -11,9 +11,10 @@ import * as config from "./apm"
 import Command from "./command"
 import Login from "./login"
 import * as request from "./request"
+import type { CliOptions, RunCallback } from "./apm-cli"
 
 export default class Unstar extends Command {
-  parseOptions(argv) {
+  parseOptions(argv: string[]) {
     const options = yargs(argv).wrap(Math.min(100, yargs.terminalWidth()))
     options.usage(`\
 
@@ -54,7 +55,7 @@ Run \`apm stars\` to see all your starred packages.\
     })
   }
 
-  run(options, callback) {
+  run(options: CliOptions, callback: RunCallback) {
     options = this.parseOptions(options.commandArgs)
     const packageNames = this.packageNamesFromArgv(options.argv)
 
diff --git a/src/upgrade.ts b/src/upgrade.ts
index 2159ba3..6c8701f 100644
--- a/src/upgrade.ts
+++ b/src/upgrade.ts
@@ -19,15 +19,19 @@ import * as Packages from "./packages"
 import * as request from "./request"
 import { tree } from "./tree"
 import * as git from "./git"
+import { PackageMetadata } from "./packages"
+import type { CliOptions, RunCallback } from "./apm-cli"
 
 export default class Upgrade extends Command {
+  private atomDirectory = config.getAtomDirectory()
+  private atomPackagesDirectory: string
+
   constructor() {
     super()
-    this.atomDirectory = config.getAtomDirectory()
     this.atomPackagesDirectory = path.join(this.atomDirectory, "packages")
   }
 
-  parseOptions(argv) {
+  parseOptions(argv: string[]) {
     const options = yargs(argv).wrap(Math.min(100, yargs.terminalWidth()))
     options.usage(`\
 
@@ -69,7 +73,7 @@ available updates.\
     return packages
   }
 
-  getIntalledPackage(name) {
+  getIntalledPackage(name: string) {
     const packageDirectory = path.join(this.atomPackagesDirectory, name)
     if (fs.isSymbolicLinkSync(packageDirectory)) {
       return
@@ -98,12 +102,12 @@ available updates.\
     }
   }
 
-  folderIsRepo(pack) {
+  folderIsRepo(pack: PackageMetadata) {
     const repoGitFolderPath = path.join(this.atomPackagesDirectory, pack.name, ".git")
     return fs.existsSync(repoGitFolderPath)
   }
 
-  getLatestVersion(pack, callback) {
+  getLatestVersion(pack: PackageMetadata, callback) {
     const requestSettings = {
       url: `${config.getAtomPackagesUrl()}/${pack.name}`,
       json: true,
@@ -153,7 +157,7 @@ available updates.\
     })
   }
 
-  getLatestSha(pack, callback) {
+  getLatestSha(pack: PackageMetadata, callback: Function) {
     const repoPath = path.join(this.atomPackagesDirectory, pack.name)
     return config.getSetting("git", (command) => {
       if (command == null) {
@@ -176,12 +180,12 @@ available updates.\
     })
   }
 
-  hasRepo(pack) {
+  hasRepo(pack: PackageMetadata) {
     return Packages.getRepository(pack) != null
   }
 
-  getAvailableUpdates(packages, callback) {
-    const getLatestVersionOrSha = (pack, done) => {
+  getAvailableUpdates(packages: PackageMetadata[], callback: Function) {
+    const getLatestVersionOrSha = (pack: PackageMetadata, done) => {
       if (this.folderIsRepo(pack) && pack.apmInstallSource?.type === "git") {
         return this.getLatestSha(pack, (err, sha) => done(err, { pack, sha }))
       } else {
@@ -189,16 +193,21 @@ available updates.\
       }
     }
 
-    return async.mapLimit(packages, 10, getLatestVersionOrSha, function (error, updates) {
-      if (error != null) {
-        return callback(error)
-      }
+    return async.mapLimit(
+      packages,
+      10,
+      getLatestVersionOrSha,
+      (error, updates: { latestVersion?: string; sha?: string; pack: PackageMetadata }[]) => {
+        if (error != null) {
+          return callback(error)
+        }
 
-      updates = updates.filter((update) => update.latestVersion != null || update.sha != null)
-      updates.sort((updateA, updateB) => updateA.pack.name.localeCompare(updateB.pack.name))
+        updates = updates.filter((update) => update.latestVersion != null || update.sha != null)
+        updates.sort((updateA, updateB) => updateA.pack.name.localeCompare(updateB.pack.name))
 
-      return callback(null, updates)
-    })
+        return callback(null, updates)
+      }
+    )
   }
 
   promptForConfirmation(callback) {
@@ -230,7 +239,7 @@ available updates.\
     return async.waterfall(installCommands, callback)
   }
 
-  run(options, callback) {
+  run(options: CliOptions, callback: RunCallback) {
     const { command } = options
     options = this.parseOptions(options.commandArgs)
     options.command = command
diff --git a/src/view.ts b/src/view.ts
index e4778cd..47de80e 100644
--- a/src/view.ts
+++ b/src/view.ts
@@ -13,9 +13,10 @@ import Command from "./command"
 import * as config from "./apm"
 import * as request from "./request"
 import { tree } from "./tree"
+import type { CliOptions, RunCallback } from "./apm-cli"
 
 export default class View extends Command {
-  parseOptions(argv) {
+  parseOptions(argv: string[]) {
     const options = yargs(argv).wrap(Math.min(100, yargs.terminalWidth()))
     options.usage(`\
 
@@ -110,7 +111,7 @@ View information about a package/theme in the atom.io registry.\
     })
   }
 
-  run(options, callback) {
+  run(options: CliOptions, callback: RunCallback) {
     options = this.parseOptions(options.commandArgs)
     const [packageName] = Array.from(options.argv._)