Is there any downside to using ts-node in dev env but tsc in production?

[rohit-malhotra]

Since the way typescript compilation works in tsc is different from ts-node, what are the downsides or possible gotchas that may happen due to this?

[cspotcode]

No big gotchas. Generally the differences are in typechecking, which you can/should avoid by using tsc to typecheck and keeping ts-node fast with --transpile-only. This is a personal recommendation; other people will disagree with me. Ultimately, the decision is yours to make. You can also avoid the major typechecking differences with --files.

ts-node forces a few compiler options to be enabled, overriding your tsconfig.json

ts-node/src/configuration.ts

Lines 7 to 17 in 03355c1

	/**
	* TypeScript compiler option values required by `ts-node` which cannot be overridden.
	*/
	const TS_NODE_COMPILER_OPTIONS = {
	sourceMap: true,
	inlineSourceMap: false,
	inlineSources: true,
	declaration: false,
	noEmit: false,
	outDir: '.ts-node',
	};

These are pretty harmless changes. For example, enabling sourcemaps does not affect the emitted JS code other than appending a //# sourcemap comment, and you may already have sourcemaps enabled.

We intentionally avoid deviating from tsc behavior much -- despite the community asking us to do so often -- because we want to remain pretty close in behavior to tsc. It's not perfect, there are differences, but the goal is to be very close to tsc so that you can use ts-node as a development convenience and use tsc for production to reap the performance benefits of pre-compilation.

[cspotcode]

I forgot to mention, we also make these changes to your tsconfig.

ts-node/src/configuration.ts

Lines 19 to 42 in 03355c1

	/*
	* Do post-processing on config options to support `ts-node`.
	*/
	function fixConfig(ts: TSCommon, config: _ts.ParsedCommandLine) {
	// Delete options that *should not* be passed through.
	delete config.options.out;
	delete config.options.outFile;
	delete config.options.composite;
	delete config.options.declarationDir;
	delete config.options.declarationMap;
	delete config.options.emitDeclarationOnly;
	// Target ES5 output by default (instead of ES3).
	if (config.options.target === undefined) {
	config.options.target = ts.ScriptTarget.ES5;
	}
	// Target CommonJS modules by default (instead of magically switching to ES6 when the target is ES6).
	if (config.options.module === undefined) {
	config.options.module = ts.ModuleKind.CommonJS;
	}
	return config;
	}

As you can see, the deleted options should not affect the emitted .js, and you can explicitly specify target and module in your tsconfig to avoid our defaults.