resolve-chunk plugin for webpack

Installation

npm install @microsoft/resolve-chunk-plugin --save-dev

Overview

This is a webpack plugin that looks for calls to resolveChunk with a chunk name, and returns the chunk ID. It's useful for referencing a chunk without making webpack coalesce two chunks.

Plugin

To use the plugin, add it to the plugins array of your Webpack config. For example:

import { ResolveChunkPlugin } from '@microsoft/resolve-chunk-plugin';

{
  plugins: [
    new ResolveChunkPlugin()
  ]
}

Background

Note that the following explanation of Webpack compilation is simplified and intentionally ignores some edge cases for the sake of simplicity

When you wish to split code into a separate physical file in Webpack, you call a function called require.ensure. The webpack compiler detects instances of these function calls and splits the code that you specify into a separate "chunk" and wires some code up to download and evaluate that chunk. For example:

Code you write:

require.ensure(
  ['./myModule'],
  (require: ((path: string) => IMyModule)) => {
    const myModule: IMyModule = require('./myModule');
    myModule.doStuff();
  },
  'my-chunk'
);

Code Webpack produces:

// Note that the "require" on the following line is never used. It is actually passed as undefined.
//  This may be a bug in webpack.
__webpack_require__.e(3).then((function (require) {
  var myModule = __webpack_require__(172);
  myModule.doStuff();
});

The produced code can be written by hand, and, in some cases, must be written by hand to avoid some side-effects of using Webpack's special functions.

In this example, a couple of "magic" numbers show up. The 3 in __webpack_require__.e(3) is the ID of the named "my-chunk", and the 172 in __webpack_require__(172) is the ID of the ./myModule module. Webpack provides a function called require.resolveWeak to a module's ID, but no such OOB function exists for resolving the ID of a named chunk. For example, you could write this code (equivalent to the code above):

Code you write:

__webpack_chunk_load__(3).then(() => {
  const myModule: IMyModule = __webpack_require__(require.resolveWeak('./myModule');
  myModule.doStuff();
});

Code Webpack produces:

__webpack_require__.e(3).then((function () {
  var myModule = __webpack_require__(172);
  myModule.doStuff();
});

Notice that we had to hardcode the chunk ID (3), but we were able to use the webpack require.resolveWeak function to get the module's ID.

This plugin solves the issue of hardcoding chunk IDs by providing a similar piece of syntactic sugar called resolveChunk. This function is NOT require.resolveChunk in order to avoid conflicting with the require type in TypeScript. The same example code could be written this way if this plugin is installed:

Code you write:

__webpack_chunk_load__(resolveChunk('my-chunk')).then(() => {
  const myModule: IMyModule = __webpack_require__(require.resolveWeak('./myModule');
  myModule.doStuff();
});

Code Webpack produces:

__webpack_require__.e(3).then((function () {
  var myModule = __webpack_require__(172);
  myModule.doStuff();
});

Please note that in order to use resolveChunk, the chunk must have been created by calling require.ensure somewhere else with the chunk's name.