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108 lines
3.0 KiB
108 lines
3.0 KiB
4 weeks ago
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# is-file-esm
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> Determines whether a Node file is a Module (`import`) or a Script (`require`)
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## Algorithm
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Determining the module system of a file comes from three inputs, the `type` field
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of the closest `package.json` to that file, the file extension (`.js`, `.mjs` or `.cjs`)
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and the lesser know `--input-type` command-line flag. The latter only applies to
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dyamic input (via STDIN, `--eval` or `--print` flags) so is not considered with this library.
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So to determine whether a file is an esm file (e.g. native EcmaScript modules) or not,
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we use the following procedure:
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```
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read package.json for "type" field,
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if type is "module"
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if answer.mjs -> module
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if answer.js -> module
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if answer.cjs -> script
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if type is "commonjs"
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if answer.mjs -> module
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if answer.js -> script
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if answer.cjs -> script
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if type is not set
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if answer.mjs -> module
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if answer.js -> script
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if answer.cjs -> script
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```
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## API
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The `is-file-esm` module provides synchronous, awaitable (promise-based) and callback based APIs.
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In each case the Result object has the following shape:
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```js
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{
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esm: Boolean, // true if file is a Module, false if it is a Script
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type: String, // the determined package.json type, may be undefined, 'module', or 'commonjs'
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extType: String, // the file extension type, may be 'c', 'm' or 'j'
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path: String, // the input path
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pkgPath: String // the path to the package.json from which the type was determined
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}
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```
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### Awaitable (promise-based)
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#### `await isFileEsm(path) => Result`
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```js
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import isFileEsm from 'is-file-esm'
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const { esm, path } = await isFileEsm('/path/to/file.js')
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if (esm) console.log(`File ${path} is a Module`)
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else console.log(`File ${path} is a Script`)
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```
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### Callback-style
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#### `isFileEsm(path, cb(err, Result))`
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```js
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const isFileEsm = require('is-file-esm')
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isFileEsm('/path/to/file.js', (err, result) => {
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if (err) {
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console.error(err)
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return
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}
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if (result.esm) console.log(`File ${result.path} is a Module`)
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else console.log(`File ${result.path} is a Script`)
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})
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```
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### Synchronous
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#### `isFileEsm.sync(path) => Result`
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```js
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import isFileEsm from 'is-file-esm'
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const { esm, path } = isFileEsm.sync('/path/to/file.js')
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if (esm) console.log(`File ${path} is a Module`)
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else console.log(`File ${path} is a Script`)
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```
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### Test
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```sh
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npm test
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```
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```
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test/index.js ..................................... 213/213
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total ............................................. 213/213
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213 passing (927.584ms)
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ok
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----------|----------|----------|----------|----------|-------------------|
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File | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s |
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----------|----------|----------|----------|----------|-------------------|
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All files | 100 | 100 | 100 | 100 | |
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index.js | 100 | 100 | 100 | 100 | |
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----------|----------|----------|----------|----------|-------------------|
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```
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### License
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MIT
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