Differences between ES modules and CommonJS:

1. No require, exports, or module.exports

2. No __filename or __dirname

3. No Addon Loading

4. No require.resolve

5. No NODE_PATH

6. No require.extensions

7. No require.cach

1.import

import 导入的方式：

1. file URLS

import './test.mjs?query=1' // loads ./test.mjs with query of "?query=1"

2. data imports

• text/javascript for ES modules
• application/json for JSON
• application/wasm for Wasm

3. node imports

import fs from 'node:fs/promises'

import './test.mjs?query=1'

import 'data:text/javascript,console.log("hello!")'
// import _ from 'data:application/json,"world!"' with { type: 'json' }

2.import.meta

1. import.meta.url 当前文件的绝对路径

2. import.meta.resolve 获取模块的绝对路径（类似于 path.resolve, 但该 API 依赖较高的 node 版本）

https://nodejs.org/docs/latest/api/esm.html#importmetaresolvespecifier

const dependencyAsset = import.meta.resolve('component-lib/asset.css');
// file:///app/node_modules/component-lib/asset.css
import.meta.resolve('./dep.js');
// file:///app/dep.js

在目前的版本中，如果要获取 __dirname，可以使用：

const _dirname = path.dirname(url.fileURLToPath(import.meta.url))

console.log(import.meta)

// __dirname is not defined in ES module scope
// import path from 'node:path'
// console.log(path.resolve(__dirname, './1.import.meta.mjs'))

import { fileURLToPath } from 'url'
import { dirname } from 'path'
const __filename = fileURLToPath(import.meta.url)
const __dirname = dirname(__filename)
console.log(__dirname) // Logs the directory name of the current module

3.await

// await is only valid in async functions and the top level bodies of modules
const five = await Promise.resolve(5)

/*
Top-level await:

在ES模块中，await可以在顶层使用。
*/

// works
export const five = await Promise.resolve(5)

/*
If a top level await expression never resolves, the node process will exit with a 13 status code.

[status code](https://nodejs.org/docs/latest/api/process.html#exit-codes)
*/
import { spawn } from 'node:child_process'
import { execPath } from 'node:process'
spawn(execPath, [
  '--input-type=module',
  '--eval',
  // Never-resolving Promise:
  'await new Promise(() => {})',
]).once('exit', (code) => {
  console.log(code) // Logs `13`
})