How to generate .d.ts from a js string?

Question

Does anyone know how to generate a .d.ts from a string, e.g. "export const foo = 42"?

The API reference:

https://github.com/microsoft/TypeScript/wiki/Using-the-Compiler-API

shows how to generate the compiled .js from a string, but to generate the .d.ts it only gives references for how to do it using a filesystem.

The typescript playground does exactly this, however (and without any network traffic, so it's not writing files on some server and extracting the .d.ts), so it's somehow possible.

Aleksey L. · Accepted Answer · 2021-12-12 17:56:33Z

2

You can override writeFile and readFile of CompilerHost (similar to example in the wiki):

const ts = require("typescript");

const source = "export const foo = 42";
const options = {
  emitDeclarationOnly: true,
  declaration: true,
};

let dts;
const host = ts.createCompilerHost(options);
host.writeFile = (fileName, contents) => (dts = contents);
host.readFile = () => source;

const program = ts.createProgram(["foo"], options, host);
program.emit();

console.log(dts);

"foo" is a fake source file.

answered Dec 12, 2021 at 17:56

Aleksey L.

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