Improve types and type coverage

index.js

@@ -1,6 +1,6 @@
 'use strict';
 
-/** @template T */
+/** @template [T=undefined] */
 class ErrorWithCause extends Error {
   /**
    * @param {string} message
@@ -9,8 +9,13 @@ class ErrorWithCause extends Error {
   constructor (message, { cause } = {}) {
     super(message);
 
+    /** @type {string} */
     this.name = ErrorWithCause.name;
-    this.cause = cause;
+    if (cause) {
+      /** @type {T} */
+      this.cause = cause;
+    }
+    /** @type {string} */
     this.message = message;
   }
 }

package.json

@@ -22,6 +22,7 @@
     "check:installed-check": "installed-check -i dependency-check -i installed-check",
     "check:lint": "eslint .",
     "check:tsc": "tsc",
+    "check:type-coverage": "type-coverage --detail --strict --at-least 97 --ignore-files 'test/*'",
     "check": "run-s clean && run-p check:*",
     "clean:declarations": "rm -rf $(find . -maxdepth 2 -type f -name '*.d.ts')",
     "clean": "run-p clean:*",
@@ -50,7 +51,7 @@
     "@types/verror": "^1.10.5",
     "@voxpelli/eslint-config": "^12.0.2",
     "@voxpelli/eslint-config-jsdoc-ts": "^0.3.1",
-    "@voxpelli/tsconfig": "^3.0.0",
+    "@voxpelli/tsconfig": "^3.1.0-0",
     "c8": "^7.10.0",
     "chai": "^4.3.4",
     "chai-string": "^1.5.0",
@@ -70,7 +71,8 @@
     "installed-check": "^5.0.0-1",
     "mocha": "^9.1.3",
     "npm-run-all": "^4.1.5",
-    "typescript": "~4.4.4",
+    "type-coverage": "^2.19.0",
+    "typescript": "^4.5.1-rc",
     "verror": "^1.10.1"
   }
 }

test/error.spec.js

@@ -25,12 +25,12 @@ describe('ErrorWithCause', () => {
   it('should handle missing options object', () => {
     const err = new ErrorWithCause('Foo');
 
-    err.should.have.property('cause', undefined);
+    err.should.not.have.property('cause');
     err.should.have.property('message', 'Foo');
   });
 
   it('should handle empty options object', () => {
-    (new ErrorWithCause('Foo', {})).should.have.property('cause', undefined);
+    (new ErrorWithCause('Foo', {})).should.not.have.property('cause');
   });
 
   it('should produce a proper stack trace', () => {

test/find.spec.js

@@ -98,6 +98,7 @@ describe('findCauseByReference()', () => {
     const cause = new ErrorWithCause('Foo');
     const err = new ErrorWithCause('Bar', { cause });
 
+    // @ts-ignore
     cause.cause = err;
 
     const result = findCauseByReference(err, SubError);

test/message.spec.js

@@ -73,6 +73,7 @@ describe('messageWithCauses()', () => {
     const cause = new ErrorWithCause('Foo');
     const err = new ErrorWithCause('Bar', { cause });
 
+    // @ts-ignore
     cause.cause = err;
 
     const result = messageWithCauses(err);

test/stack.spec.js

@@ -86,6 +86,7 @@ describe('stackWithCauses()', () => {
     cause.stack = 'abc123';
     err.stack = 'xyz789';
 
+    // @ts-ignore
     cause.cause = err;
 
     const result = stackWithCauses(err);