Closure to TypeScript `.d.ts` generator
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mprobst Refactor `declareNamespace` filtering.
The previous double negated nested condition was hard to read or reason
Latest commit 00d1742 Sep 18, 2018

Clutz - Closure to TypeScript Declarations (.d.ts) generator.

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This project uses the Closure Compiler to parse Closure-style JSDoc type annotations from ES5/ES2015 code, and generates a suitable TypeScript type definition file (.d.ts) for the exported API.

The intent is to allow TypeScript code to import libraries written with Closure-style type declarations. Having the clutz generated declarations allows type-checking in the TypeScript compiler and IDE tooling (for highlighting errors and type-sensitive auto-complete) as if the imported code was written in TypeScript.

Example usage

We don't offer a binary distribution, so first you need to build from source:

$ npm install
$ gradle build installDist

You can use Clutz from the command line using the wrapper script produced by Grade or by executing the JAR file in build/libs/ yourself. Here is a sample execution:

$ PATH=$PATH:./build/install/clutz/bin
$ clutz path/to/my/source1.js path/to/my/source2.js ...
        --externs path/to/closure-compiler/externs/es3.js path/to/closure-compiler/externs/es5.js ...
        -o out.d.ts

This creates TypeScript type definitions in out.d.ts for all the closure types discovered in the inputs. Symbols which were declared with goog.provide('x') may be imported in TypeScript as import x from 'goog:x';. For full explanation of what TypeScript types are produced for different Closure usages, see the .js and .d.ts files in src/test/com/google/javascript/clutz.

When compiling TypeScript code that depends on the closure code, include the src/resources/closure.lib.d.ts file along with out.d.ts.

Note that clutz requires that your code can be compiled with Closure Compiler. If you get errors, try reproducing them without clutz, by compiling your code with Closure alone. The arguments for invoking clutz are intentionally similar to the arguments for invoking the Closure compiler. You can find the additional compiler flags that clutz passes to Closure Compiler in src/main/java/com/google/javascript/clutz/ If the failure is reproducible this way, then you have a closure type error in your code (or a bug in Closure Compiler).

Supported Version of TypeScript

Clutz produces declaration files that are guaranteed to be accepted by a version of TypeScript 2.7.2. The current test suite runs against the version of typescript in npm-shrinkwrap.json, so that is always a good choice.


You can run the test suite with:

$ ./gradlew test

Pass the environment variable UPDATE_GOLDENS=y to update the golden files.

Gents - Closure to TypeScript converter

This repository also hosts gents - tool that generates TypeScript code out of Closure annotated .js. We host it in this repo together with clutz because they both wrap Closure Compiler to get the type information. As such gents shares clutz restriction that it only accepts code that is valid well-typed Closure JavaScript.

Details about some specific conversions follow:

Module Conversion

gents converts Closure goog.module and goog.provide module/namespaces into TypeScript modules. On the exporting side, it converts export assignments into TypeScript export statements. On the importing side, it converts goog.require statements into TypeScript imports. Due to naming issues, this may result in the renaming of the imported symbols.

// file a.js
exports = function(n) { return n; };

// file b.js
provided.B.val = 4;

// file c.js
var A = goog.require('mod.A');
var B = goog.require('provided.B');

/** @type {number} */
var num = A(B.val);

Is converted to:

// file a.ts
export const A = function(n) { return n; };

// file b.ts
export const val = 4;

// file c.ts
export {};
import {A} from "./a";
import * as B from "./b";

let num: number = A(B.val);

Class Conversion

gents converts @constructor annotated functions and goog.defineClass into ES6 class declarations. Additionally, it moves all prototype and static method/field declarations into the class.

 * @param {number} n
 * @constructor
function A(n) {
  /** @type {number} */
  this.num = n;

/** @return {number} */ = function() { return 4; };
/** @return {boolean} */ = function() { return false; };
/** @type {boolean} */
A.x = true;

Is converted to:

class A {
  num: number;
  static x: boolean = true;

  constructor(n: number) {
    this.num = n;
  foo(): number {
    return 4;
  static bar(): boolean {
    return false;

Type Conversion

gents converts JSDoc annotated JavaScript into the proper TypeScript declaration. Note that just like with classes, gents only converts explicitly annotated types. This is to make sure gents doesn't accidentally aggressively infer the types of every variable and generate giant type declarations.

Known Issues and TODOs

Github issues