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Tsickle - TypeScript to Closure Translator Linux build Windows build

Tsickle converts TypeScript code into a form acceptable to the Closure Compiler. This allows using TypeScript to transpile your sources, and then using Closure Compiler to bundle and optimize them, while taking advantage of type information in Closure Compiler.

What conversion means

A (non-exhaustive) list of the sorts of transformations Tsickle applies:

  • inserts Closure-compatible JSDoc annotations on functions/classes/etc
  • converts ES6 modules into goog.module modules
  • generates externs.js from TypeScript d.ts (and declare, see below)
  • declares types for class member variables
  • translates export * from ... into a form Closure accepts
  • converts TypeScript enums into a form Closure accepts
  • reprocesses all jsdoc to strip Closure-invalid tags

In general the goal is that you write valid TypeScript and Tsickle handles making it valid Closure Compiler code.

Warning: work in progress

We already use tsickle within Google to minify our apps (including those using Angular), but we have less experience using tsickle with the various JavaScript builds that are seen outside of Google.

We would like to make tsickle usable for everyone but right now if you'd like to try it you should expect to spend some time debugging and reporting bugs.


  • Execute npm i to install the dependencies.


Project Setup

Tsickle works by wrapping tsc. To use it, you must set up your project such that it builds correctly when you run tsc from the command line, by configuring the settings in tsconfig.json.

If you have complicated tsc command lines and flags in a build file (like a gulpfile etc.) Tsickle won't know about it. Another reason it's nice to put everything in tsconfig.json is so your editor inherits all these settings as well.


Run tsickle --help for the full syntax, but basically you provide any tsickle specific options and use it as a TypeScript compiler.

Differences from TypeScript

Closure and TypeScript are not identical. Tsickle hides most of the differences, but users must still be aware of some differences.


Any declaration in a .d.ts file, as well as any declaration tagged with declare ..., is intepreted by Tsickle as a name that should be preserved through Closure compilation (i.e. not renamed into something shorter). Use it any time the specific string names of your fields are significant. That would most often happen when the object either coming from outside your program, or being passed out of the program.


declare interface JSONResult {
    username: string;
let r = JSON.parse(input) as JSONResult;

By adding declare to the interface (or if it were in a .d.ts file), Tsickle will inform Closure that it must use exactly the field name .username (and not e.g. .a) in the output JS. This matters for this example because the input JSON probably uses the string 'username' and not whatever name Closure would invent for it. (Note: declare on an interface has no additional meaning in pure TypeScript.)

Exporting decorators

An exporting decorator is a decorator that has @ExportDecoratedItems in its JSDoc.

The names of elements that have an exporting decorator are preserved through the Closure compilation process by applying an @export tag to them.


/** @ExportDecoratedItems */
function myDecorator() {
  // ...

class DoNotRenameThisClass { ... }


Gulp tasks

  • gulp watch executes the unit tests in watch mode (use gulp test.unit for a single run),
  • gulp test.e2e executes the e2e tests,
  • guld test.golden executes the golden tests,
  • gulp test.check-format checks the source code formatting using clang-format,
  • gulp test runs unit tests, e2e tests and checks the source code formatting.

Environment variables

Export the environment variable UPDATE_GOLDENS=1 to have the test suite rewrite the golden files when you run it.

Export the environment variable TEST_FILTER, a regex, to limit the end-to-end tests (found in test_files/...) run tests with a name matching the regex.


On a new branch, run npm version <major|minor|patch|...> -m 'rel: %s' (see npm help version for details) to update the version in package.json, commit the changes, and create a git tag. Push the branch, get it reviewed and merged, then run npm publish from the master branch (you must be logged into the angular shared npm account).