ESM import.meta All In One
ESM import.meta All In One
获取 ES Module 的
meta
原数据
import.meta
The import.meta meta-property
exposes context-specific metadata
to a JavaScript module.
It contains information
about the module, such as the module's URL
.
import.meta.url
The full URL
to the module, includes query
parameters and/or hash
(following the ? or #).
In browsers
, this is either the URL from which the script
was obtained (for external scripts), or the URL of the containing document (for inline scripts
).
In Node.js
, this is the file path
(including the file://
protocol).
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/import.meta
使用场景
- 使用
ESM
在 Node.js 中实现__dirname
功能, 获取模块所在的文件夹
的绝对路径
- ...
import fs from 'node:fs';
import path from 'node:path';
import { fileURLToPath } from 'node:url';
const __filename = fileURLToPath(import.meta.url);
const __dirname = path.dirname(__filename);
console.log(`✅ import.meta.url =`, import.meta.url, typeof import.meta.url)
console.log(`✅ __filename =`, __filename, typeof __filename)
console.log(`✅ __dirname`, __dirname, typeof __dirname)
errors
solutions
- 浏览器
<script type="module">
<script type="module">
console.log(`import.meta.url =`, import.meta.url);
</script>
<!-- 或 -->
<script src="./main.mjs" type="module"></script>
// main.mjs
console.log(`✅ import.meta.url =`, import.meta.url);
- Node.js
import.meta.resolve
const absolutePath = await import.meta.resolve(specifier[, parent]);
// main.mjs
const resolvedPath = await import.meta.resolve('./helper.mjs');
https://nodejs.org/docs/latest-v15.x/api/esm.html#esm_import_meta
https://deno.land/manual@v1.36.3/runtime/import_meta_api
demos
ESM 中实现
__dirname
import fs from 'node:fs';
import path from 'node:path';
import { fileURLToPath } from 'node:url';
// import fs from 'fs';
// import path from 'path';
// import { fileURLToPath } from 'url';
// create one custom `__dirname`, because it doesn't exist in es-module env.
// use `import.meta.url` to get the current module's URL, ✅
// then get the module's folder absolute path
const __filename = fileURLToPath(import.meta.url);
const __dirname = path.dirname(__filename);
const dir = path.resolve(path.join(__dirname, 'upload');
if (!fs.existsSync(dir)) {
fs.mkdirSync(dir);
}
// OR
if (!fs.existsSync(dir)) {
fs.mkdirSync(dir, {
mode: 0o744, // Not supported on Windows. Default: 0o777
});
}
CJS
__dirname
const fs = require('fs');
const path = require('path');
const dir = path.resolve(path.join(__dirname, 'upload');
if (!fs.existsSync(dir)) {
fs.mkdirSync(dir);
}
// OR
if (!fs.existsSync(dir)) {
fs.mkdirSync(dir, {
mode: 0o744, // Not supported on Windows. Default: 0o777
});
}
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node:fs
vs fs
import fs from 'node:fs';
import fs from 'fs';
node:
类似https://
,file://
是一种通信协议 ❓
Modules: node:module
API
ESM
// module.mjs
// In an ECMAScript module
import { builtinModules as builtin } from 'node:module';
CJS
// module.cjs
// In a CommonJS module
const builtin = require('node:module').builtinModules;
https://nodejs.org/dist/latest-v18.x/docs/api/module.html
refs
https://stackoverflow.com/questions/67554506/what-are-the-nodefs-nodepath-etc-modules
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