is-file-esm

> Determines whether a Node file is a Module (import) or a Script (require)

Algorithm

Determining the module system of a file comes from three inputs, the type field
of the closest package.json to that file, the file extension (.js, .mjs or .cjs)
and the lesser know --input-type command-line flag. The latter only applies to
dyamic input (via STDIN, --eval or --print flags) so is not considered with this library.

So to determine whether a file is an esm file (e.g. native EcmaScript modules) or not,
we use the following procedure:

``
read package.json for "type" field,
if type is "module"
if answer.mjs -> module
if answer.js -> module
if answer.cjs -> script
if type is "commonjs"
if answer.mjs -> module
if answer.js -> script
if answer.cjs -> script
if type is not set
if answer.mjs -> module
if answer.js -> script
if answer.cjs -> script
`

API

The is-file-esm module provides synchronous, awaitable (promise-based) and callback based APIs.

In each case the Result object has the following shape:

`js
{
esm: Boolean, // true if file is a Module, false if it is a Script
type: String, // the determined package.json type, may be undefined, 'module', or 'commonjs'
extType: String, // the file extension type, may be 'c', 'm' or 'j'
path: String, // the input path
pkgPath: String // the path to the package.json from which the type was determined
}
`

$3

#### await isFileEsm(path) => Result

`js
import isFileEsm from 'is-file-esm'
const { esm, path } = await isFileEsm('/path/to/file.js')
if (esm) console.log(File ${path} is a Module)
else console.log(File ${path} is a Script)
`

$3

#### isFileEsm(path, cb(err, Result))

`js
const isFileEsm = require('is-file-esm')
isFileEsm('/path/to/file.js', (err, result) => {
if (err) {
console.error(err)
return
}
if (result.esm) console.log(File ${result.path} is a Module)
else console.log(File ${result.path} is a Script)
})
`

$3

#### isFileEsm.sync(path) => Result

`js
import isFileEsm from 'is-file-esm'
const { esm, path } = isFileEsm.sync('/path/to/file.js')
if (esm) console.log(File ${path} is a Module)
else console.log(File ${path} is a Script)
`

$3

`sh
npm test
`

`
test/index.js ..................................... 213/213
total ............................................. 213/213

213 passing (927.584ms)

ok
----------|----------|----------|----------|----------|-------------------|
File | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s |
----------|----------|----------|----------|----------|-------------------|
All files | 100 | 100 | 100 | 100 | |
index.js | 100 | 100 | 100 | 100 | |
----------|----------|----------|----------|----------|-------------------|
``

$3

MIT