Fetch polyfill with webpack

webpack.js

var webpack = require('webpack');
var HtmlWebpackPlugin = require('html-webpack-plugin');
var path = require('path');
var folders = {
    APP: path.resolve(__dirname, '../app'),
    BUILD: path.resolve(__dirname, '../build'),
    BOWER: path.resolve(__dirname, '../bower_components'),
    NPM: path.resolve(__dirname, '../node_modules')
};

var config = {
    entry: {
        app: [
            'webpack/hot/dev-server',
            "./js/app.js"
        ]
    },
    debug: true,
    resolve: {
        extensions: ['', '.js', '.jsx', '.scss'],
        alias: {
            //'es6-promise': path.join(folders.NPM, 'es6-promise', 'es6-promise.js'),
            //'fetch': path.join(folders.NPM, 'whatwg-fetch', 'fetch.js'),
        }
    },
    stats: {
        colors: true,
        reasons: true,
    },
    output: {
        path: __dirname + '/build',
        publicPath: '/',
        filename: '[name].[hash].js',
        chunkFilename: '[id].[hash].js'
    },
    module: {
        loaders: [
            {
                test: /\.s?css$/,
                exclude: /node_modules/,
                loaders: [
                    'style',
                    'css',
                    'autoprefixer?browsers=last 2 version',
                    'sass?' + ['outputStyle=nested'].join('&')
                ]
            },
            { test: /\.jsx?$/, loaders: ['react-hot', 'babel'], exclude: /node_modules/ },
            { test: /\.json$/, loader: 'json' },
        ]
    },
    plugins: [
        new webpack.HotModuleReplacementPlugin(),
        new webpack.ProvidePlugin({
            'Promise': 'es6-promise', // Thanks Aaron (https://gist.github.com/Couto/b29676dd1ab8714a818f#gistcomment-1584602)
            'fetch': 'imports?this=>global!exports?global.fetch!whatwg-fetch'
        }),
        //new webpack.optimize.CommonsChunkPlugin('app', null, false),
        new webpack.NoErrorsPlugin(),
        new HtmlWebpackPlugin({
            template: path.resolve('./', 'index.html'),
            webpackDevServer: '/webpack-dev-server.js'
        })
    ]
};

module.exports = config;

thanks, fetch works perfectly here :)
Can you explain how do you inject fetch as webpack plugin ?

This is super awesome @Couto! 👍

If it's okay with you I'll write a quick blog post about including polyfills like fetch in webpack.

Don't forget to install imports-loader and exports-loader, if you use this.

npm install imports-loader exports-loader --save

The ProvidePlugin works by hooking into the parser, and adding a dependency whenever it sees an identifier matching a property name of the object it's instantiated with. So with the above config, whenever the parser hits fetch, it will add a dependency on whatwg-fetch.

Since es6-promise isn't a valid identifier, I believe it should be:

        new webpack.ProvidePlugin({
            'Promise': 'es6-promise',
            'fetch': 'imports?this=>global!exports?global.fetch!whatwg-fetch'
        }),

When I changed es6-promise to Promise in my project, the output grew by ~3k (gzipped), so I believe you need to use Promise.

So I wanted to add the fetch polyfill so I added the dependencies (es6-promise, fetch, import-loader, export-loader) and these lines to my Webpack config file. But when running it in Safari 9 i get the following error from fetch.

TypeError: Object is not a constructor (evaluating 'new Promise')

Which seems to indicate Promise is not present when fetch is used. According to caniuse this version of Safari has support for Promises. So it might be es6-promise that is messing with Promise. Anyone else experiencing this?

If I remove the line:
'Promise': 'es6-promise',
Everything works as expected in Safari but I lose support for IE and Opera Mini since I'm not using a Promise polyfill.

Maybe this is a concern that should be raised over at es6-promise. Anyone know how I can solve this problem? 😄

@Andersos I've had some success on IE9 by using the following snippet:

new webpack.ProvidePlugin({
  Promise: 'imports?this=>global!exports?global.Promise!es6-promise',
  fetch: 'imports?this=>global!exports?global.fetch!whatwg-fetch',
  React: 'react'
})

So far this works because es6-promise calls the polyfill() automatically, right after the UMD snippet.

Also:
I haven't tested but, I'm pretty sure you can import the es6-promise and call the polyfill() function, something like:

import {polyfill} from 'es6-promise';
polyfill();

right at the top of your app's entry point.

Hi @Couto I have had the same issues as @Andersos on firefox 37 and ie 11. As you suggested I am now importing the package and then calling the polyfill() method at the top of my app.js; however does this mean the polyfill will be added even if the browser implements Promise api?

@Nosherwan @Couto @Andersos I was having the same issues with Promise and ended up simplifying it to the following:

new webpack.ProvidePlugin({
    'Promise': 'exports?global.Promise!es6-promise',
    'fetch': 'exports?self.fetch!whatwg-fetch'
})

This works in Chrome, Safari, and IE. The polyfills for both fetch and Promise are only used when needed.

I case anyone runs into this in the future.. if you are calling window.fetch inside your code. Use 'window.fetch' your config.

new webpack.ProvidePlugin({
    'Promise': 'exports?global.Promise!es6-promise',
    'window.fetch': 'exports?self.fetch!whatwg-fetch'
})

Why do we need to add this as a plugin to webpack? Can't we just do import ('fetch') in our code to get the benefits?

In my testing this increased the bundle filesize by about 3kb compared to just importing the polyfills in my entrypoint. No clue why, perhaps it's skipped over by Webpack's de-duping?

Unfortunately this means even new browsers will use the Promise polyfill 😢

My mistake, that's intended: jakearchibald/es6-promise#148

@finbarmaginn I was wondering the same thing, but I think you have the benefit of deciding when to polyfill based on the environment. E.g. you probably don't want to polyfill promises when testing in Node.js because newer versions support them.

Is this still the preferred method to polyfill Promise and does it cause any errors? re: https://github.com/babel/babel-loader#custom-polyfills-eg-promise-library

I am curious just today I have learned that at least in babel 6 there is a 'babel-polyfill' (provides es6 env) that can be imported via the entry option in webpack.config.js like so:

var path = require('path');
var webpack = require('webpack');

module.exports = {
  entry: [
    'babel-polyfill',
    './src/main'
  ],
  output: {
      publicPath: '/',
      filename: 'main.js'
  },
  devtool: 'source-map',
  module: {
    loaders: [
      {
        test: /\.js$/,
        include: path.join(__dirname, 'src'),
        loader: 'babel-loader',
        query: {
          presets: ["es2015","react"],  
        }
      }
    ]
  },
  debug: true
};

Would this not make es6-promise polyfill redundant, and maybe it is smart enough to use browser implementation if provided?

Was wondering the same thing…

babel-polyfill does not appear to include a fetch polyfill, so you'd still need to use this.

Wouldn't simply including it in entry be a better approach? There is actually a use case where the demonstrated method will fail, for example if you use Webpack server side with externals: [nodeExternals()], you would be forced to use entry anyways because external modules would not see fetch as being defined. So it seems it would be more consistent to use entry here as well.

After double checking, this approach is actually incorrect and will not polyfill fetch properly, the correct approach is to configure whatwg-fetch on your Webpack entry configuration, like such:

module.exports = {
   entry: ['whatwg-fetch', './app/js']
};

This will fix issues where using a 3rd party that expect fetch will not find it with the approach of this gist. This is also consistent with the way babel documents using a polyfill with Webpack and does not require the extra loaders.

I have opened a PR with fetch so they stop referring to this solution: github/fetch#331

@Nosherwan @silvenon you should not include a Promise polyfill if you use babel-polyfill, the correct configuration would then be:

module.exports = {
   entry: ['babel-polyfill', 'whatwg-fetch', './app/js']
};

Has anyone had success adding this when entry is an object?

@simonsmith Does this not work for you?

entry: {
    demo: ['whatwg-fetch', './app']
  },

@tarikjn
Works for me too, thanks!

@Couto ganda truta! 👍

🐟

@tarikjn i am getting a Exception thrown and not caught in IE11 when i use babel-polyfill instead of es6 promise .

entry: ['babel-polyfill', 'whatwg-fetch','./src/main.js'],

but this works perfect in IE11

entry: ['es6-promise', 'whatwg-fetch','./src/main.js']

Is there a way to have the polyfills loaded from a seperated chunk?

I wish that when a browser is lacking a feature it loads the predeclared polyfill (which would be put in a chunk by webpack). So that the final bundle size does not contain all the polyfills.

Is this possible somehow?

@vikas5914, I'm getting the exact same. Did you solve this in the end, as I would rather keep using babel-polyfill

Adding polyfills through entry - defines them in global scope. If you own an application (SPA for example), I think It's Ok, but if you are working on the library, I don't recommend this approach.

if you use webpack 2 you need to change import -> import-loader and export -> export-loader

new webpack.ProvidePlugin({
  fetch: 'imports-loader?this=>global!exports-loader?global.fetch!whatwg-fetch'
})

Can we use webpack.ProvidePlugin to conditionally load polyfills? Essentially load polyfills if browser don't support natively.

+1