tsc-watch

What is tsc-watch?

The tsc-watch npm package is a utility that allows you to run the TypeScript compiler (tsc) in watch mode and execute custom scripts when certain events occur, such as when compilation starts, succeeds, or fails. This is particularly useful for automating tasks during development, such as running tests or restarting a server.

What are tsc-watch's main functionalities?

Run TypeScript compiler in watch mode

This feature allows you to run the TypeScript compiler in watch mode, which means it will automatically recompile your TypeScript files whenever they change. The `--onSuccess` flag specifies a command to run whenever the compilation succeeds. In this example, it runs a Node.js script located at `./dist/index.js`.

tsc-watch --onSuccess "node ./dist/index.js"

Run custom scripts on compilation failure

This feature allows you to specify a command to run whenever the TypeScript compilation fails. In this example, it simply echoes 'Compilation Failed!' to the console.

tsc-watch --onFailure "echo Compilation Failed!"

Run custom scripts on compilation start

This feature allows you to specify a command to run whenever the TypeScript compilation starts. In this example, it echoes 'Compilation Started!' to the console.

tsc-watch --onCompilationStarted "echo Compilation Started!"

Other packages similar to tsc-watch

nodemon

Nodemon is a utility that monitors for any changes in your source and automatically restarts your server. It is language-agnostic and can be used with any executable, not just TypeScript. Unlike tsc-watch, nodemon does not handle TypeScript compilation by itself; you would need to use it in conjunction with the TypeScript compiler.

ts-node-dev

ts-node-dev is a development tool that combines ts-node and nodemon. It watches for changes in TypeScript files and restarts the Node.js process automatically. Unlike tsc-watch, ts-node-dev directly executes TypeScript files without needing a separate compilation step.

webpack

Webpack is a module bundler that can be configured to watch for changes in your files and recompile your project. With the appropriate loaders, it can handle TypeScript files. Webpack is more complex and powerful than tsc-watch, offering features like code splitting and hot module replacement.

README

The nodemon for TypeScript

tsc-watch starts the installed TypeScript compiler (tsc) with --watch parameter, with the ability to react to compilation status. tsc-watch was created to allow an easy dev process with TypeScript. Commonly used to restart a node server, similar to nodemon but for TypeScript.

Anything that you can do with tsc you can do with tsc-watch, the only difference is that tsc-watch can react to compilation status.

Argument	Description
--onSuccess COMMAND	Executes COMMAND on every successful compilation.
--onFirstSuccess COMMAND	Executes COMMAND on the first successful compilation.
--onEmit COMMAND	Executes debounced COMMAND on every emitted file, ignoring unchanged files and disregards compilation success or failure.
--onEmitDebounceMs DELAY	Delay by which to debounce --onEmit (default: 300).
--onFailure COMMAND	Executes COMMAND on every failed compilation.
--onCompilationStarted COMMAND	Executes COMMAND on every compilation start event (initial and incremental).
--onCompilationComplete COMMAND	Executes COMMAND on every successful or failed compilation.
--maxNodeMem	Calls node with a specific memory limit max_old_space_size, to use if your project needs more memory.
--noColors	By default tsc-watch adds colors the output with green on success, and in red on failure. Add this argument to prevent that.
--noClear	In watch mode the tsc compiler clears the screen before reporting Add this argument to prevent that.
--signalEmittedFiles	Will run tsc compiler with --listEmittedFiles, but hiding TSFILE lines. Use it to enable file_emitted event, while keeping tsc stdout silent.
--silent	Do not print any messages on stdout.
--compiler PATH	The PATH will be used instead of typescript compiler. Default is typescript/bin/tsc

Notes:

• That all the above COMMANDs will be killed on process exit. (Using SIGTERM)

• A COMMAND is a single command and not multi command like script1.sh && script2.sh

• Any child process (COMMAND) will be terminated before creating a new one.

Install

npm install tsc-watch --save-dev

## for command-line usage
npm install -g typescript tsc-watch

Usage

From Command-Line

## Watching a project (with tsconfig.json)
tsc-watch --onSuccess "node ./dist/server.js"

## Beep on failure
tsc-watch --onFailure "echo Beep! Compilation Failed"

## Watching a single file
tsc-watch server.ts --outDir ./dist --onSuccess "node ./dist/server.js"

## Custom compiler
tsc-watch --onSuccess "node ./dist/server.js" --compiler my-typescript/bin/tsc

From npm script

"dev-server": "tsc-watch --noClear -p ./src/tsconfig.json --onSuccess \"node ./dist/server.js\"",

From javascript

You can see a detailed example here

The client is implemented as an instance of Node.JS's EventEmitter, with the following events:

• started - Emitted upon the compilation start (initial or incremental).
• first_success - Emitted upon first successful compilation.
• subsequent_success - Emitted upon every subsequent successful compilation.
• compile_errors - Emitted upon every failing compilation.
• file_emitted - Emitted upon every file transpiled if --listEmittedFiles is used.

Once subscribed to the relevant events, start the client by running watch.start()

To kill the client, run watch.kill()

Example usage:

// Using CommonJS:
const { TscWatchClient } = require('tsc-watch/client');
// Using ES6 import:
import { TscWatchClient } from 'tsc-watch/client';

const watch = new TscWatchClient();

watch.on('started', () => {
  console.log('Compilation started');
});

watch.on('first_success', () => {
  console.log('First success!');
});

watch.on('success', () => {
  // Your code goes here...
});

watch.on('compile_errors', () => {
  // Your code goes here...
});

watch.start('--project', '.');

try {
  // do something...
} catch (e) {
  watch.kill(); // Fatal error, kill the compiler instance.
}

Notes:

• The (onSuccess) COMMAND will not run if the compilation failed.
• The (onEmit) COMMAND will not run if the compilation succeeded with no changed files, unless it is the first success.
• The (onEmit) COMMAND will run even if the compilation failed, but emitted changed files.
• The (onEmit) COMMAND will not run 100 times for 100 files, due to --onEmitDebounce
• The (onEmit) COMMAND is not cancelling the onSuccess/onFirstSuccess/onFailure/onCompilationComplete/onCompilationStarted commands and vice versa.
• tsc-watch is using the currently installed TypeScript compiler.
• tsc-watch is not changing the compiler, just adds the new arguments, compilation is the same, and all other arguments are the same.

Changelog

v6.2.1 - 13/11/2024

• bug fix: Fixed new version of Typescript clear codes. thanks to @staszekj