Debugging NestJS app in NRWL NX workspace – David Votrubec

Debugging can save you ton of time. But sometimes to set up debugging configuration correctly can be a nightmare. There are several common gotchas which may trick you.

Code is in Typescript, but NodeJS in debugger does not understand its syntax.
You use combination of .ts and .js files with import or export statement
Debugger does not attach, and breakpoints are ignored
False positive detection of debug mode (flag --inspect or --inspect-brk did not work for my use case)

NRWL NX is a great tool, but somewhat it complicated debugging of NestJS app. At least for me 🙂 So after a couple of hours of trial and error, this is what finally works for me.

launch.json

Notice that --experimental-modules is turned on. Also notice usage of pwa-node, and specification of env variables.

{
	"version": "0.2.0",
	"configurations": [
		{
			"name": "Debug my NESTJS app",
			"type": "pwa-node",
			"request": "launch",
			"args": ["src/main.ts"], // Path to main entry file
			"runtimeArgs": ["--require", "ts-node/register", "--require", "tsconfig-paths/register", "--experimental-modules"],
			"cwd": "${workspaceRoot}",
			"internalConsoleOptions": "openOnSessionStart",
			"env": {
				"NODE_ENV": "local",
				"NODE_PORT": "8000",
				"TS_NODE_PROJECT": "tsconfig.debug.json", // Specify the tsconfig to use. See content of it below.
				"IS_DEBUG_MODE": "true" // Custom env variable to detect debug mode
			},
			"sourceMaps": true,
			"console": "internalConsole",
			"outputCapture": "std",
			"resolveSourceMapLocations": [
				"${workspaceFolder}/**",
				"!**/node_modules/**" // Disable the "could not read source map" error for node_modules
			]
		}
	]
}

tsconfig.debug.json

{
	"extends": "./tsconfig.json",
	"compilerOptions": {
		"outDir": "../../dist/out-tsc",
		"types": ["node"],
		"emitDecoratorMetadata": true,
		"target": "es6",
		"module": "commonjs",
		"importHelpers": false,
		"allowJs": true // Fixes combination of .js and .ts files
	},
	"exclude": ["**/*.spec.ts"],
	"include": ["**/*.ts"]
}

Detection of debug mode inside running application

export function isInDebugMode(): boolean {
	// can not rely on "--inspect" flag, because that is used when launched via NX. Even in standard launching.
	// "--inspect-brk" flag did not work either
	// So in normal situation you would use this:
	// return /--inspect/.test(process.execArgv.join(' '));

	// Workaround using ENV variable
	return process.env['IS_DEBUG_MODE'] === 'true';
}

Fix of path to files in debug mode

Normally the asset files would be in workspace/dist/appname/assets folder. That applies when application is launched normally via nx serve appname command. But when you launch app in debug mode, then the __dirname variable may resolve differently, and then the app crashes.

So this is my workaround.

export class SomeFileService {
	private readonly encoding = 'utf8';

	// Different path in debug mode and standard mode
	private readonly pathToFile = isInDebugMode()
		? path.resolve('./', 'src/assets/configs/predefined-programs.json')
		: path.resolve(__dirname, 'assets/configs/predefined-programs.json');

        async readFile(): Promise<T> {
		return await readFile(this.pathToFile, this.encoding)
			.then((data) => {
				const parsedData = JSON.parse(data);
				return parsedData;
			})
			.catch((err) => {
				console.error('SomeFileService: Error reading data from ' + this.pathToFile, err);
			});
	}
}

Happy coding.