javascript - Make webpack's library output compatible with babel6

Babel's 6th version changes the functioning of export default and in particular its relation with monjs require.

To summarise, while until babel5, require('module') where giving the default export of the module, it now always returns the module object containing all of the exports of the module. If one only wants the default, he/she must use require('module').default. As explained here, there is very good reasons behind this and the aim of this question is not to break or hack this behaviour.

However, if one is building a library, he/she usually does not want to distribute a module but the export value of his library (e.g. a function, whatever module system is used internally). This is well dealt with by webpack and the output.library configuration when using monjs or AMD. Because prior babel's versions allowed the default export to be required with monjs, babel was also patible with this mechanism. However it is not the case anymore: the library now always provides an es6 module object.

Here is an example.

src/main.js

export default "my lib content";

webpack.config.js

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

module.exports = {
  entry: {
    lib: [ path.resolve(__dirname, "src/main.js") ],
  },
  output: {
    path: path.join(__dirname, "dist"),
    filename: "mylib-build.js",
    library: 'myLib'
  },
  module: {
    loaders: [
      {
        test: /\.js$/,
        loader: "babel",
        include: path.join(__dirname, "src"),
        query: { presets: ['es2015'] }
      }
    ]
  }
};

test.html

<html>
<head></head>
<body>
<script src="dist/mylib-build.js"></script>
<!-- `myLib` will be attached to `window` -->
<script>
  console.log(JSON.stringify(myLib)); // { default: "my lib content" }
</script>
</body>
</html>

This is a very simple example but I obviously want the export of mylib to be the string "my lib content" instead of { default: "my lib content" }.

One solution could be to create an export source file in monjs to perform the transformation:

module.exports = require('./main').default;

However I find this solution quite poor. One should be able to solve it at the pilation level, without changing the source code. Any idea?

Babel's 6th version changes the functioning of export default and in particular its relation with monjs require.

Here is an example.

src/main.js

export default "my lib content";

webpack.config.js

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

module.exports = {
  entry: {
    lib: [ path.resolve(__dirname, "src/main.js") ],
  },
  output: {
    path: path.join(__dirname, "dist"),
    filename: "mylib-build.js",
    library: 'myLib'
  },
  module: {
    loaders: [
      {
        test: /\.js$/,
        loader: "babel",
        include: path.join(__dirname, "src"),
        query: { presets: ['es2015'] }
      }
    ]
  }
};

test.html

<html>
<head></head>
<body>
<script src="dist/mylib-build.js"></script>
<!-- `myLib` will be attached to `window` -->
<script>
  console.log(JSON.stringify(myLib)); // { default: "my lib content" }
</script>
</body>
</html>

This is a very simple example but I obviously want the export of mylib to be the string "my lib content" instead of { default: "my lib content" }.

One solution could be to create an export source file in monjs to perform the transformation:

module.exports = require('./main').default;

However I find this solution quite poor. One should be able to solve it at the pilation level, without changing the source code. Any idea?

Share Improve this question edited May 23, 2017 at 12:32 CommunityBot 11 silver badge asked Nov 12, 2015 at 18:40 Quentin Roy 7,8872 gold badges33 silver badges52 bronze badges

"One should be able to solve it has a pilation option and without having to update the source code. Any idea?" Not quite sure what kind of answer you expect. If you think this should be a pilation option, then you should suggest it to the developer(s). – Felix Kling Commented Nov 12, 2015 at 18:44
Webpack configuration is pretty powerful. There is many different plugins, and many different parameters for all loaders. – Quentin Roy Commented Nov 12, 2015 at 18:49
For example, if one only use default export, he could use babel-plugin-transform-es2015-modules-monjs and transform all his es6 packages to monjs. – Quentin Roy Commented Nov 12, 2015 at 18:51
You are going to do it in a wrong way. Babel changed its behavior to be more patible with the spec, and you want to break it again. Now you can make an implicit bridge between ES6 and CommonJS. That thing module.exports = require('./main').default, cause fewer errors and WTFs, rather than previous sneaky module.exports = exports.default – just-boris Commented Nov 21, 2015 at 19:06
1 @vvo Not yet unfortunately... So I had to use the export solution to give webpack a monjs module instead. – Quentin Roy Commented Dec 9, 2015 at 20:17

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3 Answers 3

Sorted by: Reset to default 6

Was just going at this my self. Whether one like to call it a workaround or solution, there seem to be a Babel plugin that "solve it".

Using the plugin babel-plugin-add-module-exports as referenced in https://stackoverflow./a/34778391/1592572

Example config

var webpackOptions = {
    entry: {
        Lib1: './src/Lib1.js',
        Lib2: './src/Lib2.js'
    },
    output: {
        filename: "Master.[name].js",
        library: ["Master","[name]"],
        libraryTarget: "var"
    },
    module: {
        loaders: [
            {
                loader: 'babel',
                query: {
                    presets: ['es2015'],
                    plugins: ["add-module-exports"]
                }
            }
        ]
    }
};

This yields Master.Lib1 to be lib1 instead of Master.Lib1.default.

Webpack 2 now supports es6 modules which partially solves this issue. Migrating from webpack 1 to webpack 2 is relatively painless. One just needs to remember to disable babel's es6 module to monjs conversion to make this work:

.babelrc

{
  "presets": [
    ["es2015", {"modules": false}]
  ]
}

However, unfortunately, it does not work properly with export default (but an issue is opened, hopefully a solution will be released eventually).

EDIT

Good news! Webpack 3 supports the output.libraryExport option that can be used to directly expose the default export:

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

module.exports = {
  entry: {
    lib: [ path.resolve(__dirname, "src/main.js") ],
  },
  output: {
    path: path.resolve(__dirname, "dist"),
    filename: "mylib-build.js",
    library: "myLib",
    // Expose the default export.
    libraryExport: "default"
  },
  module: {
    loaders: [
      {
        test: /\.js$/,
        loader: "babel",
        include: path.resolve(__dirname, "src")
      }
    ]
  }
};

You can use this solution (this is more like workaround, but it allow you to keep your sources from change):

There is a loader called callback-loader. It allow you to change your sources in a build time by calling a callback and put a result instead of it. In other words you can turn all you require('module') into a require('module').default automatically in a build time.

Here is your config for it:

var webpackConfig = {
    module: {
        loaders: [
            { test: /\.js$/, exclude: /node_modules/, loader: 'callback' },
            ...
        ]
    },
    ...
    callbackLoader: {
        require: function() {
            return 'require("' + Array.prototype.join.call(arguments, ',') + '").default';
        }
    }
};

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3 Answers 3

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