babel-preset-njs

A Babel preset for transforming JavaScript code with modern language features into code compatible with njs (NGINX JavaScript). This preset includes support for all the ECMAScript features that TypeScript supports (Stage 3+) — see Plugins for a complete list.

Installation

# using npm:
npm install --save-dev babel-preset-njs
# or using yarn:
yarn add --dev babel-preset-njs

Usage

With a Configuration File (Recommended)

{
  "presets": ["babel-preset-njs"]
}

{
  "presets": [
    ["babel-preset-njs", { "assumeArrayIterables": false }]
  ]
}

Via CLI

babel --presets babel-preset-njs script.js

Via Node API

require('@babel/core').transform('code', {
  presets: [require('babel-preset-njs')],
})

Options

assumeArrayIterables

boolean, defaults to true

Assume that all iterables used in for...of loops, array spread syntax and array destructuring are arrays. This produces more compact and significantly more performant code, but it will fail in runtime if the iterable is not an array.

TypeScript transpiler uses the same approach for ES5 target when downlevelIteration is disabled. It also indicates error when the iterable is not an array.

It sets the following plugin options:

• for-of: assumeArray

• spread: loose

• destructuring: loose

asyncHelpers

'external', 'local', 'inline'

Toggles how async-to-promises injects its helpers:

• 'external' — injects import from babel-plugin-transform-async-to-promises/helpers into each file with async/await

• 'local' — injects the needed helper functions into each file with async/await

• 'inline' — inlines the needed helper code in place of each occurrence of async/await

Defaults to 'external' if Rollup or webpack is detected, otherwise 'local'.

• async-to-promises: externalHelpers, inlineHelpers

looseClasses

boolean, defaults to true

Define class methods and properties using a simple assignment expression instead of Object.defineProperty(). This produces more compact and performant code, but it might produce unexpected results in some (corner) cases. TypeScript transpiler uses the same approach.

It sets the following plugin options:

• classes: loose

• class-properties: loose

• private-property-in-object: loose

looseObjectRestSpread

boolean, defaults to true

Transform object rest/spread properties using Object.assign() instead of Babel’s objectSpread helper. This produces more compact and performant code, but it might produce unexpected results in some (corner) cases (when overwriting read-only target property). TypeScript transpiler uses the same approach.

It sets the following plugin options:

• object-rest-spread: loose

looseParameters

boolean, defaults to true

In loose mode, function parameters with default values will be counted into the arity of the function. This is not spec behaviour where these parameters do not add to function arity, but it produces more compact and performant code. TypeScript transpiler uses the same approach.

It sets the following plugin options:

• parameters: loose

Plugins

The list of included Babel plugins is available here.

References

• njs ECMAScript Compatibility

License

This project is licensed under MIT License.