generate d.ts programmatically (in memory)

Question

I know that we could use tsc --declaration --emitDeclarationOnly --outFile index.d.ts to generate declaration file. But how can I generate it programmatically? For example:

import ts from 'typescript'
const dts = await ts.generateDdeclaration(/* tsconfig.json */);
// then do some stuff with dts, like in webpack plugin

I don't want d.ts output into a file. I am kind of stuck and don't know how to get started

Answer 1

To generate it programmatically you will need to:

1. Setup a ts.Program based on a tsconfig.json file.
2. Emit the program by calling Program#emit with emitOnlyDtsFiles set to true and provide a custom writeFile callback to capture the output in memory.

Here's an example using @ts-morph/bootstrap because I have no idea how to easily setup a program with a tsconfig.json file using only the TypeScript Compiler API (it takes a lot of code from my understanding and this is easier):

// or import as "@ts-morph/bootstrap" if you're using node/npm
import {
  createProjectSync,
  ts,
} from "https://deno.land/x/ts_morph@12.0.0/bootstrap/mod.ts";

const project = createProjectSync({
  tsConfigFilePath: "tsconfig.json",
});

const files = new Map<string, string>();
const program = project.createProgram();
program.emit(
  undefined,
  (fileName, data, writeByteOrderMark) => {
    if (writeByteOrderMark) {
      data = "\uFEFF" + data;
    }
    files.set(fileName, data);
  },
  undefined,
  /* emitOnlyDtsFiles */ true,
  // custom transformers could go here in this argument
);

// use files here