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Path aliases with TypeScript in Node.js

larswaechter profile image Lars Wächter Updated on ・2 min read

Some days ago I included path aliases in my TypeScript Node.js projects. Since they make the code look much cleaner in my opinion I like to show you how to setup these in a project.

The problem

In Node.js (or TS/JS in general) you can import single modules into your code.
This might look the following:

import { User } from '../../user/model';
import { Article } from '../../article/model';

import { Cache } from '../../../../cache';
import { MongoDB } from '../../../../mongodb';

Noticed these dots ('../') to access upper modules?

The problem we have here is that the deeper your project tree is the more '../' are required to access modules in higher layers. Actually, this doesn't look very beautiful to be honest. Fortunately we can change that.

The solution: path aliases

What are path aliases?

In TypeScript you can avoid these "bad" looking imports with the help of path aliases. With path aliases you can declare aliases that map to a certain absolute path in your application.

Here a quick example:

import { User } from '@modules/user/model';
import { Article } from '@modules/article/model';

import { Cache } from '@services/cache';
import { MongoDB } from '@services/mongodb';

In this case our two aliases are

  • @modules that maps to './src/rest/modules'
  • @services that maps to './src/services'

Setup

Let's get into it and setup some path aliases. Note that I won't explain how to setup a TypeScript project in Node.js. I assume that you did this already.

Imagine we have the following project structure:

folder structure
└───src
   │
   └───rest
   │   │
   │   └───modules
   │   │   │
   │   │   └───article
   │   │   │
   │   │   └───user
   │   │
   │   │   server.ts
   │
   │
   └───services
   │   │    cache.ts
   │   │    mongodb.ts
   │    
   │   index.ts

Step 1: Update tsconfig.json

First of all, we have to declare the path aliases in our tsconfig file

"baseUrl": "./src",
"paths": {
    "@modules/*": ["rest/modules/*"],
    "@services/*": ["services/*"]
}

Now, you can use the new path aliases for module imports in your application. There occur any errors in your IDE (in my case VSC) or when you compile the code.

However, we are not done yet. When you try compile the TS code into JS you won't see any errors. But as soon as you run your compiled JS code you will get an error:

For example:

Error: Cannot find module '@modules/user'

That's because JS can't resolve the modules for the declared path aliases.

Step 2: Install module-alias package

Next, we'll install an npm package called module-alias

npm i --save module-alias

This module registers the path aliases in the compiled JS files. Therefor we need to make some changes to our package.json:

"_moduleAliases": {
    "@modules": "dist/rest/modules",
    "@services": "dist/services"
  }

Note that 'dist' is the folder where the compiled JS files are located.

Last but not least we have to register the path aliases in our application.
Add the following line at the top of your startup file:

import 'module-alias/register';

Finally, when you compile and execute the code you shouldn't see any import errors.

Here you can find some examples for path aliases in a side project I'm currently working on.

Posted on by:

larswaechter profile

Lars Wächter

@larswaechter

23 | Germany | CS Student | Software Developer

Discussion

markdown guide
 

Had an issue with zeit/pkg because the generated files (in the dist folder) still had the @/dir/to/your/file references, which pkg could not handle.

In case you need to change your js files from the @/your-file back into their ../../../your-file form, you can use ef-tspm to bring it back. Note, if you do so, you won't need to deal with the extra steps for the module-alias specified above. Trade-off is you have an additional build step. So first you would tsc to build the typescript code, then ef-tspm to properly remove the module aliases.

 

I've just released a new package Alias HQ, which allows you to reuse your js/tsconfig.json path aliases in Webpack, Jest, Rollup, or any other library.

Just call hq.get('<library name>') in the config file you want to use aliases in, and you're done:

github.com/davestewart/alias-hq

 

Thanks!

Also I find out that if we have webpack in project we just use resolve.alias option:


  resolve: {
    extensions: ['.js', '.ts', '.tsx', '.styl'],
    mainFields: ['module', 'browser', 'main'],
    alias: Object.keys(tsconfig.compilerOptions.paths).reduce((aliases, aliasName) => {

      aliases[aliasName] = path.resolve(__dirname, `src/${tsconfig.compilerOptions.paths[aliasName][0]}`)

      return aliases
    }, {})
  },
 

Thank you! I read several posts about using path aliases and thought it was perfect for my project, but I hit the *cannot find module" issue. I was banging my head off the desk all afternoon. It's been really difficult to find anything on this.

 

Thanks for the article!

However, to utilize this solution we have to define the aliases in 2 locations: tsconfig.json and package.json. Is it possible to avoid this duplication?

 

These aliases -- which I've grown used to on the frontend frameworks which use webpack -- are a VERY welcome addition to writing typescript on the backend (or in other library code). My one question comes down to testing. I have a library with hundreds of tests but right now none of them run because I'm using Mocha/Chai with ts-node and I'm not sure but I think that ts-node is not able to use the alias.

The command I use is:

./node_modules/.bin/mocha --no-timeouts --require ts-node/register --exit

This is a pretty standard way of testing as it allows you to test directly on the source rather than needing to transpile before testing.

 

How complex is the folder organization for your source code? I had looked into this but it doesn't have as much value with flatter source-orgs

 

The complexity of my folder organization depends on the project. Mostly I have some root folders like: config, rest, services that I declare path aliases for. Inside these I have my components for example.

 

How cool is that eh! thanks for posting.

 
 
 

Hey,

I have followed your tutorial by the letter and even restarted code editor but keep getting the error, no matter what I do

 
 

the original error that article is about
'module is not found'

 

Thanks a lot for sharing, I was getting crazy with the issues where modules were not being found.

 

I found that using extension to import marketplace.visualstudio.com/items... works good enough and not require much logic.

 
 

I couldn't get the aliases working without first building the project since they are registered using the dist folder. Feels hacky. Is there a way around this ?