Emitter

There are two emitters provided with the TypeScript compiler:

  • emitter.ts: this is the emitter you are most likely to be interested in. Its the TS -> JavaScript emitter.
  • declarationEmitter.ts: this is the emitter used to create a declaration file (a .d.ts) for a TypeScript source file (a .ts file).

We will look at emitter.ts in this section.

Usage by program

Program provides an emit function. This function primarily delegates to emitFiles function in emitter.ts. Here is the call stack:

  1. Program.emit ->
  2.     `emitWorker` (local in program.ts createProgram) ->
  3.         `emitFiles` (function in emitter.ts)

One thing that the emitWorker provides to the emitter (via an argument to emitFiles) is an EmitResolver. EmitResolver is provided by the program’s TypeChecker, basically it a subset of local functions from createChecker.