Babel Preset njs

0.7.0 verified Sat Apr 25 auth: no javascript

A Babel preset for transforming modern JavaScript (up to ES2021) into code compatible with njs (NGINX JavaScript). Current stable version is 0.7.0, targeting njs ≥ 0.7.0, with peer dependency on @babel/core ^7.0.0-0. Key differentiator: provides a curated set of Babel plugins for features not yet supported by njs (e.g., classes, for-of, object rest/spread), while skipping transformations for features njs already supports (e.g., arrow functions, block scoping, destructuring). Ideal for developers writing njs scripts with modern JS syntax.

Common errors

error ReferenceError: require is not defined in ES module scope ↓

cause Using require() to load the preset in an ES module environment.

fix

Use import babelPresetNjs from 'babel-preset-njs' or use require in a CommonJS context.

error SyntaxError: Unexpected token '.' (when using optional chaining) ↓

cause Optional chaining (?.) is not yet supported by njs and not included in the preset's plugins.

fix

Avoid optional chaining; use if statements or add @babel/plugin-proposal-optional-chaining manually.

error Error: Plugin/Preset files are not allowed to export objects, only functions ↓

cause Using an older version of the preset that exports an object instead of a function.

fix

Update to babel-preset-njs@0.7.0 and ensure @babel/core is version 7+.

Warnings

breaking Version 0.7.0 requires njs ≥ 0.7.0. Older versions of njs may not work. ↓

fix Upgrade njs to at least 0.7.0 or use an older version of the preset (0.2.1 max).

gotcha The preset does NOT transform dynamic import() or generators (yield) as njs does not support them. These will fail at runtime. ↓

fix Avoid using dynamic imports and generators in njs code, or provide your own custom plugin.

deprecated Some plugins included may become unnecessary as njs evolves. Check compatibility table before upgrading. ↓

fix Review the plugin list in the preset's README to see which features are now natively supported.

Install

npm install babel-preset-njs

yarn add babel-preset-njs

pnpm add babel-preset-njs

Imports

babelPresetNjs

wrong

const babelPresetNjs = require('babel-preset-njs')

correct

import babelPresetNjs from 'babel-preset-njs'

ESM import; can also be used with require in CJS

babel-preset-njs (preset name string)
wrong
```
module.exports = { presets: [require('babel-preset-njs')] }
```
correct
```
module.exports = { presets: ['babel-preset-njs'] }
```
In Babel config, reference the preset by its name string, not by directly requiring it.
babel.config.js (using preset via string)
wrong
```
{
  "presets": ["@babel/preset-njs"]
}
```
correct
```
{
  "presets": ["babel-preset-njs"]
}
```
Do not prefix with @babel/. The preset name is exactly 'babel-preset-njs'.

Quickstart

Shows installation, Babel config, and a simple njs script using for-of and object spread, both of which are transformed by the preset.

// Install: npm install --save-dev @babel/core babel-preset-njs
// Then create babel.config.js:
module.exports = {
  presets: ['babel-preset-njs']
};

// Now write your njs script (src/index.js):
const arr = [1, 2, 3];
const obj = { a: 1, b: 2 };
const spread = { ...obj, c: 3 };
for (const x of arr) {
  ngx.log(ngx.INFO, x);
}

// Run: npx babel src/index.js --out-dir dist
// Result will be compatible with njs (e.g., for-of transpiled, object spread transformed).