Building a nestjs project in typescript is really awesome but as the project starts to grow , your directories will grow too thus making your imports lengthy like this:

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

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

Path mapping to the rescue!

TypeScript allows the use of path mapping which allows arbitrary module paths (that doesn’t start with “/” or “.”) to be specified and mapped to physical paths in the filesystem in the compiler options in tsconfig file like below:

{
  "compilerOptions": {
    ...
    "baseUrl": "./src",
    "paths": {
      "@datorama/utils/*": ["app/utils/*"],
      "@datorama/pipes/*": ["app/pipes/*"]
    }
    ...
  }
}

The first property that we must add is the baseUrl property. Notice that paths are resolved relative to baseUrl . The second property is the paths property. This tells the compiler for any module import that matches the pattern "@datorama/utils/*" , to look in the following location:

The Problem

When you run the code inline (during execution) , it works as intended but when you build it for production and try to run it, you get the following error:

Error: Cannot find module '@datorama/utils'

The issue mentioned is of execution with node.Actually the problem occurs when executing the built files with node dist/main.js, not during the build process with tsc.

The Solution

After doing some search on the problem, I came across multiple solutions.

• Using webpack
• Using Module Aliases package
• Bootstrapping tsc with explicit params

Although there are bunch of solutions above, the first and second one didn't work for me. So I went with the third one which was actually mentioned in the docs of tsconfig-paths which nest uses to resolve these paths at runtime.

To apply the solution, make a file named tsconfig-paths-bootstrap.js (The name is up to you) and copy/paste the below snippet

// tsconfig-paths-bootstrap.js

const tsConfig = require("./tsconfig.json");
const tsConfigPaths = require("tsconfig-paths");

const baseUrl = "./dist"; // Either absolute or relative path. If relative it's resolved to current working directory.
tsConfigPaths.register({
  baseUrl,
  paths: tsConfig.compilerOptions.paths,
});

Build the dist file normally as you do with tsc. After that, you can run it with

node -r ./tsconfig-paths-bootstrap.js dist/main.js

Note: Check the file name with the filename in the command and you are good to go

Shoutout to Jay McDoniel for his help.