feat: add executable for npx. See #59

Usage example: `npx merge ./foo.json ./bar.json`.

merge-cli.mjs

@@ -0,0 +1,57 @@
+#!/usr/bin/env node
+import mri from 'mri';
+import fs from 'fs';
+
+import { merge, recursive } from "./lib/index.js";
+
+const args = mri(process.argv.slice(2), {
+  alias: {
+    s: 'shallow',
+    h: 'help',
+  },
+  boolean: ['shallow', 'help'],
+});
+
+const inputFiles = args._;
+
+/*
+Why to avoid `process.exit()`:
+  see https://stackoverflow.com/a/37592669/521957
+  or https://nodejs.org/api/process.html#processexitcode.
+*/
+if (args.help) {
+  if (inputFiles.length) {
+    process.exitCode = 1;
+    console.error("You can't provide `--help` or `-h` flags and input files at the same time.")
+  } else {
+    const help = `\
+npx merge
+  [--shallow or -s] # If merge is shallow then recursion won't be used.
+  [--help or -h]
+  [file1.json file2.json ...]
+`;
+    process.stdout.write(help);
+  }
+
+} else if (!inputFiles.length) {
+
+  console.log({});
+
+} else {
+
+  const objects = inputFiles.map(
+    (path) => {
+      const json = fs.readFileSync(path, 'utf-8');
+      return JSON.parse(json);
+    }
+  );
+  const ifToClone = false;
+  let merged;
+  if (args.shallow) {
+    merged = merge(ifToClone, ...objects);
+  } else {
+    merged = recursive(ifToClone, ...objects);
+  }
+  console.log(merged);
+
+}

package.json

@@ -27,6 +27,9 @@
   "files": [
     "lib/index.d.ts"
   ],
+  "bin": {
+    "merge": "./merge-cli.mjs"
+  },
   "scripts": {
     "build": "tsc --build tsconfig.build.json",
     "check": "prettier --cache -c .",
@@ -46,5 +49,8 @@
     "prettier-plugin-sort-json": "^3.0.1",
     "typescript": "^5.2.2",
     "vitest": "^0.34.4"
+  },
+  "dependencies": {
+    "mri": "^1.2.0"
   }
 }