Use jest with Typescript, ESM and aliases

Question

I developed a module with Typescipt and ESM ("type": "module" in package.json).

I also use some path aliases, this is the tsconfig.json

{
    "compilerOptions": {
        "moduleResolution": "Node16",
        "module": "Node16",
        "target": "ES2015",
        "lib": [
            "ES2022"
        ],
        "resolveJsonModule": true,
        "strictNullChecks": true,
        "sourceMap": true,
        "declaration": false,
        "downlevelIteration": true,
        "esModuleInterop": true,
        "baseUrl": ".",
        "paths": {
            "@/*": [
                "./source/*"
            ],
            "@": [
                "./source"
            ],
            "@src/*": [
                "./source/*"
            ],
            "@src": [
                "./source"
            ],
            "@test/*": [
                "./test/*"
            ],
            "@test": [
                "./test"
            ]
        },
        "outDir": "./dist"
    },
    "include": [
        "source",
        "test"
    ]
}

And this is the jest.config.ts

import type { Config } from '@jest/types';
import { pathsToModuleNameMapper } from 'ts-jest';
import tsconfigJson from './tsconfig.json';

const config: Config.InitialOptions = {
    preset: 'ts-jest/presets/default-esm',
    testEnvironment: 'node',
    verbose: true,
    globals: {
        'ts-jest': {
            tsconfig: './tsconfig.json',
            useESM: true
        }
    },
    moduleNameMapper: pathsToModuleNameMapper(tsconfigJson.compilerOptions.paths, { prefix: '<rootDir>/' }),
    transformIgnorePatterns: ['<rootDir>/node_modules/']
};
export default config;

The problem is that, because of ESM, the modules do not work with the aliases:

 FAIL  test/suites/modules/mangleTypes.test.ts
  ● Test suite failed to run

    Configuration error:
    
    Could not locate module @src/modules/mangleTypes.js mapped as:
    /home/euber/Github/lifeware-java-mangler/source/$1.
    
    Please check your configuration for these entries:
    {
      "moduleNameMapper": {
        "/^@src\/(.*)$/": "/home/euber/Github/lifeware-java-mangler/source/$1"
      },
      "resolver": undefined
    }

    > 1 | import { mangleType, PrimitiveType } from '@src/modules/mangleTypes.js';
        | ^
      2 |
      3 | describe('Test @/modules/mangleTypes', function () {
      4 |     describe('Primitive types', function () {

      at createNoMappedModuleFoundError (node_modules/jest-resolve/build/resolver.js:900:17)
      at Object.<anonymous> (test/suites/modules/mangleTypes.test.ts:1:1)

I referenced this as a solution, but it does not work.

UPDATE I tried also like this, but it does not work

Answer 1

Eventually I managed to make it work by mixing the two solutions:

import type { Config } from '@jest/types';
import { pathsToModuleNameMapper } from 'ts-jest';
import tsconfigJson from './tsconfig.json';

function manageKey(key: string): string {
   return key.includes('(.*)') ? key.slice(0, -1) + '\\.js$' : key;
}
function manageMapper(mapper: Record<string, string>): Record<string, string> {
   const newMapper: Record<string, string> = {};
   for (const key in mapper) {
      newMapper[manageKey(key)] = mapper[key];
   }
   newMapper['^\.\/(.*)\\.js$'] = './$1';
   return newMapper;
}

const config: Config.InitialOptions = {
    preset: 'ts-jest/presets/default-esm',
    testEnvironment: 'node',
    verbose: true,
    globals: {
        'ts-jest': {
            tsconfig: './tsconfig.json',
            useESM: true
        }
    },
    moduleNameMapper: manageMapper(pathsToModuleNameMapper(tsconfigJson.compilerOptions.paths, { prefix: '<rootDir>/' }) as Record<string, string>),
    transformIgnorePatterns: ['<rootDir>/node_modules/']
};
export default config;

UPDATE:

newMapper['^\.\/(.*)\\.js$'] = './$1'; does not work in cases like ../utils/index.js. To replace the .js with everything, the regex should be changed with something like newMapper['^(.*).js$'] = '$1';.

The total code would be:

import type { Config } from '@jest/types';
import { pathsToModuleNameMapper } from 'ts-jest';
import tsconfigJson from './tsconfig.json';

function manageKey(key: string): string {
   return key.includes('(.*)') ? key.slice(0, -1) + '\\.js$' : key;
}
function manageMapper(mapper: Record<string, string>): Record<string, string> {
   const newMapper: Record<string, string> = {};
   for (const key in mapper) {
      newMapper[manageKey(key)] = mapper[key];
   }
   newMapper['^(.*).js$'] = '$1';
   return newMapper;
}

const config: Config.InitialOptions = {
    preset: 'ts-jest/presets/default-esm',
    testEnvironment: 'node',
    verbose: true,
    globals: {
        'ts-jest': {
            tsconfig: './tsconfig.json',
            useESM: true
        }
    },
    coverageProvider: 'v8',
    moduleNameMapper: manageMapper(pathsToModuleNameMapper(tsconfigJson.compilerOptions.paths, { prefix: '<rootDir>/' }) as Record<string, string>),
    transformIgnorePatterns: ['<rootDir>/node_modules/']
};
export default config;