CommonJS模块转ESM模块方法

前言：vite项目中，依赖包的加载都是基于esm模块加载的，有些依赖打包后不是esm而是CommonJS类型的，则需要由CommonJS转为esm类型。vite预构建可以默认将node_modules下的依赖包进行转换为esm类型并存放在node_modules文件夹下的.vite文件夹下，也可以自行添加路径来预构建（详见文档：https://cn.vitejs.dev/guide/dep-pre-bundling.html#customizing-the-behavior）。

对于一些老旧sdk，在vite项目中，利用pnpm link调试，就需要转包操作了。在此记录一下手动将CommonJS模块转为ESM模块的小demo。

{
  "name": "cjs_to_esm",
  "version": "1.0.0",
  "description": "",
  "type": "module",
  "scripts": {
    "build": "rollup -c"
  },
  "keywords": [],
  "author": "",
  "license": "ISC",
  "devDependencies": {
    "@rollup/plugin-commonjs": "^23.0.2",
    "rollup": "^3.2.5"
  }
}<code>{
  &quot;name&quot;: &quot;cjs_to_esm&quot;,
  &quot;version&quot;: &quot;1.0.0&quot;,
  &quot;description&quot;: &quot;&quot;,
  &quot;type&quot;: &quot;module&quot;,
  &quot;scripts&quot;: {
    &quot;build&quot;: &quot;rollup -c&quot;
  },
  &quot;keywords&quot;: [],
  &quot;author&quot;: &quot;&quot;,
  &quot;license&quot;: &quot;ISC&quot;,
  &quot;devDependencies&quot;: {
    &quot;@rollup/plugin-commonjs&quot;: &quot;^23.0.2&quot;,
    &quot;rollup&quot;: &quot;^3.2.5&quot;
  }
}</code>

import commonjs from '@rollup/plugin-commonjs';

export default {
  input: 'src/test_cjs.js',
  output: {
    file: 'output/test_esm.js',
    format: 'es'
  },
  plugins: [commonjs()]
};<code>import commonjs from '@rollup/plugin-commonjs';

export default {
  input: 'src/test_cjs.js',
  output: {
    file: 'output/test_esm.js',
    format: 'es'
  },
  plugins: [commonjs()]
};</code>