autopolyfiller

Precise polyfills. Like Autoprefixer, but for JavaScript polyfills

Autopolyfiller — Precise polyfills

This is like Autoprefixer, but for JavaScript polyfills. It scans your code and applies only required polyfills. Live example.

Assume you code is Object.keys(window). Object.keys polyfill is required to run it in any browser (include IE7). On the other hand this code can be executed on iOS 7 Safari without any polyfills. AutoPolyfiller knows about ES5 and ES6 features and their support in browsers. It can help you to write cutting-edge JavaScript without thinking about ES shims and shivs.

How it works. Step by step:

  1. Using AST matchers, it scans your code and finds all polyfills
  2. If target browsers are specified, then it reduces the list of polyfills according to the "feature database"
  3. It generates polyfills code, using polyfills database, which precisely fixes only required features

Limitations:

  • Right now it supports only safe and cross-browser polyfills from ES5, but you can add your own (see examples).
  • It can have a false-positives for some cases. For instance, autopolyfiller thinks that $('div').map() is call of Array.prototype.map. But you can exclude false-positives (see examples).

It will not work if:

  • You are evaling code with polyfills. Eg eval('Object.keys(this)')
  • You are doing something odd. Eg Object['k' + 'eys']()

autopolyfiller can be installed using npm:

npm install autopolyfiller
$ autopolyfiller lib/**/*.js -b "Explorer 7, Chrome >= 10"
$ cat lib/*.js | autopolyfiller
// Polyfills + Code 
require('autopolyfiller')().add(code) + code;

List of polyfills without browsers filtering

var autopolyfiller = require('autopolyfiller');
 
autopolyfiller()
.add('"".trim();')
.polyfills;
// ['String.prototype.trim'] 

Filtering using Autoprefixer-style browser matchers

var autopolyfiller = require('autopolyfiller');
 
autopolyfiller('IE 11', 'Chrome >= 31')
.add('"".trim();Object.create();new Promise()')
.polyfills;
// ['Promise'] 

Default autoprefixer browsers

var autopolyfiller = require('autopolyfiller'),
    autoprefixer = require('autopolyfiller');
 
autopolyfiller(autoprefixer.default)
.add('new Promise();')
.polyfills;
// ['Promise'] 

Excluding/including polyfills

var autopolyfiller = require('autopolyfiller');
 
autopolyfiller()
.exclude(['Promise'])
.include(['String.prototype.trim'])
.add('new My.Promise();')
.polyfills;
// ['String.prototype.trim'] 

Using custom parser

var autopolyfiller = require('autopolyfiller');
 
autopolyfiller()
.withParser('acorn@0.11.0', {ecmaVersion: 6})
.add('array.map(x => x * x)')
.polyfills;
// ['Array.prototype.map'] 

Adding your own polyfills

var query = require('grasp-equery').query;
var autopolyfiller = require('autopolyfiller');
 
autopolyfiller.use({
    // AST tree pattern matching 
    // It may "grep" multiply polyfills 
    testfunction (ast) {
        return query('Object.newFeature(_$)', ast).length > 0 ? ['Object.newFeature'] : [];
    },
    
    // Your polyfills code 
    polyfill: {
        'Object.newFeature': 'Object.newFeature = function () {};'
    },
    
    // This list means "apply this feature to the <list of browsers>" 
    // For more examples see https://github.com/jonathantneal/polyfill/blob/master/agent.js.json 
    support: {
        // For chrome 29 only apply Object.newFeature polyfill 
        'Chrome': [{
            only: '29',
            fill: 'Object.newFeature'
        }]
    },
    
    // This is optional. By default autopolyfiller will use 
    // polyfill's name to generate condition's code: 
    wrapper: {
        'Object.newFeature': {
            'before': 'if (!("newFeature" in Object)) {',
            'after': '}'
        }
    }
});
 
autopolyfiller()
.add('Object.create();Object.newFeature();')
.polyfills;
// ['Object.create', 'Object.newFeature'] 
 
autopolyfiller()
.add('Object.newFeature();')
.toString();
// if (!("newFeature" in Object)) { 
// Object.newFeature = function () {}; 
// } 
 
autopolyfiller('Chrome >= 20')
.add('Object.create();Object.newFeature();')
.polyfills;
// [] 

Right now Autopolyfiller aggreagates existing sources of polyfills. If you have any issues related to a polyfill code itself, please, add an issue or a pull request to the jonathantneal/polyfill.

Here is how to temporary workaround, while your issue being resolved:

var autopolyfiller = require('autopolyfiller');
 
autopolyfiller.use({
    polyfill: {
        'Function.prototype.bind': 'fixed code (!Function.prototype.bind)'
    }
});