Sharing code between projects using TypeScript and webpack

Question

I want to share code between two TypeScript projects. I don't want to publish shared code to NPM-- just want to put shared code in one project and use it in another project. I'm using Webpack and awesome-ts-loader. Current folder structure (simplified) is like this:

/devroot/
  mainProject/
    tsconfig.json
    src/
      shared/
        SomeSharedTypes.ts
  apiProject/
    tsconfig.json
    webpack.config.js
    src/
      UseSomeSharedType.ts

In UseSomeSharedType.ts, I want to be able to import types from SomeSharedTypes.ts.

I tried an obvious solution like this:

import {SharedType} from '../../mainProject/src/shared/SomeSharedTypes'

But the TS compiler gave me this error:

TS6059: File '/devroot/mainProject/src/shared/SomeSharedTypes.ts' is not under 'rootDir' '/devroot/apiProject'. 'rootDir' is expected to contain all source files.

Answer 1

The first idea I got from this Medium article, which was to use TypeScript's non-relative module imports feature. This would allow me to write my imports like this:

import {SharedType} from '@foo/SomeSharedTypes'

Using the techniques described in the article, I added a paths configuration to my tsconfig.json:

{
  "compilerOptions": {
    "baseUrl": ".",
    "paths": {
      "@foo/*": ["../mainProject/src/shared/*"],
    },
    "rootDir": "./",
    ...
  }
}

Then, again as the article recommends, for users of awesome-typescript-loader, I had to modify my webpack.config.js to add a resolution plugin:

const { TsConfigPathsPlugin } = require('awesome-typescript-loader');
. . .
  resolve: {
    extensions: ['.js', '.json', '.ts'],
    plugins: [
      new TsConfigPathsPlugin(),
    ],
  }

Important: this plugin needs to go into the resolve/plugins section of the file, not the root-level "plugins" section! If you put the resolver plugin in the wrong place, you'll get this error:

resolver.ensureHook is not a function

The steps above got me further along in the process-- TypeScript was now able to find my files!--but I still got the same error later in webpack's execution: 'rootDir' is expected to contain all source files.

After a lot more Googling, I found a solution in this StackOverflow answer: instead of a single rootDir configuration, TS has a rootDirs setting that allows multiple roots. I removed my rootDir setting from tsconfig.json and added a rootDirs setting:

"rootDirs": [
  "./",
  "../mainProject",
],

Next, I ran into a webpack error on the other-project TypeScript file I was including:

Module parse failed: Unexpected token (3:15)

You may need an appropriate loader to handle this file type.

After another hour of troubleshooting, I figured out that I need to tell the webpack loader about my new shared folder. Like this:

const path = require('path');
. . .
  rules: [
    {
      test: /\.[jt]sx?$/,
      loader: "awesome-typescript-loader",
      include: [
        __dirname,
        path.resolve(__dirname, "../mainProject/src/shared/")
      ],
      exclude: /node_modules/
    },

That worked! The nice part about this solution is that I can refactor my folder structure without changing source code. All I'd need to change is tsconfig.json and webpack.config.js.

I'm admittedly new to using webpack and TypeScript, so there may be a better solution than the one above... but the one above worked for me!

Sharing the solution here to make it easier for the next developer to find it.