TypeScript IDE provides 2 means to compile ts files :

• with a launch Run As -> Compile TypeScript.
• compile/build on save when ts file is saved.

If you select tsconfig.json, you can do Run As -> Compile TypeScript to execute tsc with the given TypeScript project to compile ts files:

If you wish to use watch mode with tsc, you can add watch property in the tsconfig.json:

Please note that watch mode doesn't work if you add new ts file. You need to stop the process and restart it.

If your project is a TypeScript project, you must enable Compile on save? from the project properties TypeScript/Compiler:

This action adds the TypeScript Builder to your project:

After that you need to activate Project / Build Automatically:

to execute TypeScript Builder when any ts files are saved.

Compile on save means compile ts file which is saved.

Here a demo with compile on save:

Build on save means compile the whole ts file of tsconfig.json when a ts file (which belongs to tsconfig.json) is saved. Pay attention, it can be slow, but if you use "outFile" inside your tsconfig.json, it can be helpful.

Here a demo with build on save: