Running Jest tests for Typescript ESM modules

typescript, programming, jest, vs code, ESM

It took me 2:30 hours to set this up and document it, it's incredibly tedious 😅

💡 If you're going to create a new npm project, take a look at my npm-package-template

`package.json` configuration

Add jest configuration information to package.json
You don't need to use jest.config.js
We fix the mandatory import.js rule that comes from ESM with the moduleNameMapper setting
We activate esm usage for typescript codes with ^.+\\\\.ts$

// {...
"jest": {
	"preset": "ts-jest",
	"testEnvironment": "node",
	"silent": true,
	"extensionsToTreatAsEsm": [
		".ts"
	],
	"moduleNameMapper": {
		"^(\\\\.{1,2}/.*)\\\\.js$": "$1"
	},
	"transform": {
		"^.+\\\\.ts$": [
			"ts-jest",
			{
				"useESM": true
			}
		]
	}
},
// ...}

`launch.json` configuration for VSCode

{
	"name": "Jest",
	"type": "node",
	"request": "launch",
	"runtimeArgs": [
		"--experimental-vm-modules", // <<< important
		"${workspaceRoot}/node_modules/.bin/jest",
		"${input:exchange}",
		"-t",
		"${input:testName}",
		"--runInBand"
	],
	"cwd": "${workspaceRoot}",
	"stopOnEntry": false,
	"console": "integratedTerminal",
	"internalConsoleOptions": "neverOpen",
	"sourceMaps": true,
	"windows": {
		"program": "${workspaceFolder}/node_modules/jest/bin/jest"
	},
	"skipFiles": ["<node_internals>/**", "**/node_modules/**"]
},