https://github.com/andarist/babel-plugin-annotate-pure-calls

This plugins helps with annotating top level functions calls with #__PURE__ comment.
https://github.com/andarist/babel-plugin-annotate-pure-calls

babel minify plugin pure side-effects uglifyjs

Last synced: 3 days ago
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This plugins helps with annotating top level functions calls with #__PURE__ comment.

• Host: GitHub
• URL: https://github.com/andarist/babel-plugin-annotate-pure-calls
• Owner: Andarist
• Created: 2017-09-22T07:16:22.000Z (over 7 years ago)
• Default Branch: main
• Last Pushed: 2025-01-07T09:38:38.000Z (16 days ago)
• Last Synced: 2025-01-13T06:03:58.189Z (10 days ago)
• Topics: babel, minify, plugin, pure, side-effects, uglifyjs
• Language: JavaScript
• Homepage:
• Size: 113 KB
• Stars: 93
• Watchers: 2
• Forks: 7
• Open Issues: 5
• Metadata Files:
  • Readme: README.md

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README

        
# babel-plugin-annotate-pure-calls

[![npm version](https://img.shields.io/npm/v/babel-plugin-annotate-pure-calls.svg)](https://www.npmjs.com/package/babel-plugin-annotate-pure-calls)

[![Build Status](https://travis-ci.org/Andarist/babel-plugin-annotate-pure-calls.svg?branch=master)](https://travis-ci.org/Andarist/babel-plugin-annotate-pure-calls)

[![npm](https://img.shields.io/npm/dm/babel-plugin-annotate-pure-calls.svg)](https://www.npmjs.com/package/babel-plugin-annotate-pure-calls)

This plugins helps with automatic **#\_\_PURE\_\_** annotation insertion. It add the comment to

[top level call](#top-level-calls) expressions and new expressions in assignment contexts (those are considered by the

plugin as **side effect free**). This helps [UglifyJS](https://github.com/mishoo/UglifyJS2) to perform dead code

elimination more efficiently and therefore reduces the bundle sizes for the consumers.

**NOTE:** It might break your code, so the caution is advised. Target audience for the plugin are libraries, which in

vast major of use cases do not introduce side effects in top level calls. That doesn't mean that application bundles

cannot benefit from the plugin.

## Pure calls

```js

// pure call

var inc = add(1)

// clearly impure - no assignment context

mutate({ prop: 'value' })

```

## Top level calls

Top level call (in terms of this plugin) is one that gets executed during script initialization. So it is every call

located at the root of a file, but also a call in an IIFE that gets executed at startup (including nested ones).

```js

var a = topLevelCall()

b = function() {

  noTopLevelCall()

}

topLevelIIFEs = (function() {

  var c = (function() {

    var d = (function() {

      var e = topLevelCall()

    })()

  })()

})()

```

## Installation

```sh

npm install --save-dev babel-plugin-annotate-pure-calls

```

## Usage

### Via `.babelrc` (Recommended)

**.babelrc**

```json

{

  "plugins": ["annotate-pure-calls"]

}

```

### Via CLI

```sh

babel --plugins annotate-pure-calls script.js

```

### Via Node API

```javascript

require('babel-core').transform('var inc = add(1)', {

  plugins: ['annotate-pure-calls'],

})

```

### Usage with babel@6

The plugin works with babel@6, you might see unmet peer dependency warning though. If you want to get rid of it, please

install `@babel/[email protected]`.

## Similar projects

- [annotate-pure-call-in-variable-declarator](https://github.com/morlay/babel-plugin-annotate-pure-call-in-variable-declarator)