esm-module-alias

An alternative to module-alias, but for esm

Project purpose

The purpose of this project is allowing developers that use esm modules to have a feature similar to the one provided by module alias.

module-alias provides the possibility to alias modules to a different path, taking the same example that is used in its documentation:

require('../../../../some/very/deep/module');

can become:

import module from '@deep/module';

To allow this, one should add some paths to the package.json, like:

{
    "aliases": {
        "@deep": "src/some/very/deep"
    }
}

The module stopped working after the introduction of the esm in NodeJS. In addition, at the moment in which this README was written, module-alias was last published three years ago.

How to pass to esm

Taken from this fantastic guide:

• Add "type": "module" to your package.json.
• Replace "main": "index.js" with "exports": "./index.js" in your package.json.
• Update the "engines" field in package.json to Node.js 14: "node": ">=14.16". (Excluding Node.js 12 as it's no longer supported)
• Remove 'use strict'; from all JavaScript files.
• Replace all require()/module.export with import/export.
• Use only full relative file paths for imports: import x from '.'; → import x from './index.js';.
• If you have a TypeScript type definition (for example, index.d.ts), update it to use ESM imports/exports.
• Optional but recommended, use the node: protocol for imports.

How to use this module to continue using the module aliases

To use this module:

• Install the module by exeuting

  $ npm install esm-module-alias

• Add the property aliases to the package.json, the same way you would have done with module-alias, for example:

  {
    "aliases": {
        "@root"      : ".",
        "@deep"      : "src/some/very/deep/directory/or/file",
        "@my_module" : "lib/some-file.js",
        "something"  : "src/foo"
    }
  }

• When you execute your script, add this module as a loader by adding --loader esm-module-alias/loader, for example:

  node --loader esm-module-alias/loader --no-warnings myscript.js # Note that --no-warnings is to disable a warning and is optional

An option if you want to create a custom loader

You can also create a custom loader, because the library exports a function that given an object like the aliases one that one would define in the package.json, will return a function that will be used as a loader.

To do so:

• Create a custom file named as you want, for instance my-loader.mjs:

  import generateAliasesResolver from 'esm-module-alias'; 
  const aliases = {
    "@root": ".",
    "@deep": "src/some/very/deep/directory/or/file",
    "@my_module": "lib/some-file.js",
    "something": "src/foo"
  };
  export const resolve = generateAliasesResolver(aliases);

• When you execute your script, add that script as a loader by adding --loader ./my-loader.mjs, for example:

  node --loader=./my-loader.mjs --no-warnings myscript.js # Note that --no-warnings is to disable a warning and is optional

What if you want to change the matching behaviour?

You can also have a custom matcher, a function that customize the behaviour of a path matching an alias.

To do so:

• Create a custom file named as you want, for instance my-loader.mjs:

  import generateAliasesResolver from 'esm-module-alias'; 
  const aliases = {
    "@root": ".",
    "@deep": "src/some/very/deep/directory/or/file",
    "@my_module": "lib/some-file.js",
    "something": "src/foo"
  };
  const matcher = (path, alias) => {
    return (path.indexOf(alias) === 0); // Your customized code
  }; 
  export const resolve = generateAliasesResolver(aliases, { matcher }); // The custom matcher is passed to the options

• When you execute your script, add that script as a loader by adding --loader ./my-loader.mjs, for example:

  node --loader=./my-loader.mjs --no-warnings myscript.js # Note that --no-warnings is to disable a warning and is optional

Tests

Tests are run with Jest and work by executing npm test with shelljs on a bunch of sample projects,

Note

This package took inspiration from a comment of a Github issue