# Tsickle - TypeScript to Closure Annotator [![Build Status](https://travis-ci.org/angular/tsickle.svg?branch=master)](https://travis-ci.org/angular/tsickle)

Tsickle processes TypeScript and adds [Closure Compiler]-compatible JSDoc
annotations. This allows using TypeScript to transpile your sources, and then
Closure Compiler to bundle and optimize them, while taking advantage of type
information in Closure Compiler.

[Closure Compiler]: https://github.com/google/closure-compiler/

## Installation

- Execute `npm i` to install the dependencies.

## Usage

### 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.

### Invocation

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.

#### `declare`

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.

Example:

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

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.)

## Development

### 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,
- `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.

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