.alias

A single configuration for path aliases to reuse across all your tools (TypeScript, webpack, Jest, etc.)

Motivation

Path alias is a powerful way to manage relative paths in your projects by replacing long import paths like this:

import result from '../../../../utils/getResult'

with a defined alias like this:

import result from 'utils/getResult'

In this example, the utils/ portion of the import is an alias that resolves to the same relative directory.

The issue is that different tools have different declaration format and capabilities of path aliases. This means that in order to reuse the same alias across development and testing you are likely to tweak multiple configuration with the setup you cannot directly reuse. This increases the maintenance cost of such setup, making aliasing expensive.

What does Dotalias do?

Dotalias establishes a single configuration format for path aliases and compiles it to configurations that different tools can understand. Effectively, it abstracts all the hassle of having to configure various tools differently. By doing so, you can finally reuse one configuration to all the tools you're using.

Getting stated

Install

$ npm install dotalias
# OR
$ yarn add dotalias

Create configuration

$ touch alias.config.js

// alias.config.js
module.exports = {
  myModule: './module.js',
}

Integrate with your tools

Refer to the integration examples to use this library with various bundlers or testing frameworks.

Configuration

You can write the alias configuration in any of the following files:

• .aliasrc
• .aliasrc.json
• .aliasrc.yaml
• .aliasrc.yml
• .aliasrc.js
• .aliasrc.cjs
• alias.config.js
• alias.config.cjs
• "alias" key in your package.json

We are using cosmiconfig to resolve the configuration file. Learn more about the way it gets resolved in the mentioned repository.

Writing configuration

The configuration file consists of keys that represent module names and values that stand for relative paths to resolve those module names.

// alias.config.js
module.exports = {
  myModule: './module.js',
}

Module paths are relative to the current working directory.

In the example above, we've created a module alias for the myModule that will resolve to a local file at ./module.js whenever imported in the code:

// Once you've configured your build tools,
// this will resolve to "./module.js".
import result from 'myModule'

In the same fashion, the configuration file can be written in various formats. Here's an example of the configuration in YAML:

myResult: './module.js'

Features

Exact module name

// alias.config.js
module.exports = {
  components: './src/components',
}

Dynamic module name

// alias.config.js
module.exports = {
  'utils/*': './src/utils/*',
}

Fallback paths

A single alias may specify multiple paths. The first matching path resolves.

// alias.config.js
module.exports = {
  'utils/*': ['src/utils/*', 'utils/*'],
}

Integrations

All the integration examples below assume you have the configuration file created at the root of your application. Whenever you import the dotalias package, it automatically reads the closest configuration and returns the necessary bindings for the integration with other tools.

webpack

In order to support dynamic import paths (i.e. wildcards), this library exports a custom webpack plugin instead of the resolve.alias configuration object.

// webpack.config.js
const { alias } = require('dotalias')

module.exports = {
  plugins: [new alias.WebpackPlugin()],
}

Rollup

// rollup.config.js
const { alias } = require('dotalias')
const aliasPlugin = require('@rollup/plugin-alias')

module.exports = {
  plugins: [
    aliasPlugin({
      ...alias.rollup,
    }),
  ],
}

Requires you to have the @rollup/plugin-alias package installed.

Jest

// jest.config.js
const { alias } = require('dotalias')

module.exports = {
  ...alias.jest,
}

TypeScript

Execute the following command in your project's root directory:

$ npx dotalias ts

This command will generate a tsconfig.alias.json partial TypeScript configuration file that you can later extend in your tsconfig.json to enable path aliases:

{
  "extends": "./tsconfig.alias.json"
}

Research

When deciding on the optimal configuration format, I've researched the path alias configurations for the most common tools I use. Below you can see a table of those tools' capabilities when it comes to path aliases:

Feature	TypeScript	webpack	Rollup	Jest	.alias
Exact paths	✅	✅	✅	✅	✅
Dynamic paths	✅	✅	✅	✅	✅
Fallbacks	✅	✅	❌ 1	✅	✅
RegExp	❌	❌ 2	✅	✅	TBA
Custom resolver	❌	❌ 2	✅	❌	TBA

¹—possible with a custom resolver; ²—possible with a custom plugin.

References

• TypeScript (paths)
• webpack (resolve.alias)
• Rollup (@rollup/plugin-alias)
• Jest (moduleNameMapper)