babel-plugin-jsdoc-closure

babel-plugin-jsdoc-closure

Transpiles JSDoc types from namepaths with module identifiers to types for Closure Compiler.

This is useful for type checking and building an application or library from a set of ES modules with Closure Compiler, without the use of any additional bundler.

Installation

npm install babel-cli babel-plugin-jsdoc-closure

Configuration

Create a .babelrc file in the root of your project to enable the plugin:

{
  "plugins": ["jsdoc-closure"],
}

Note: When your code uses Closure type casts (i.e. something like /** @type {Custom} */ (foo)), you need to configure Babel to use recast as parser and generator by modifying your .babelrc file:

{
  "plugins": ["jsdoc-closure"],
  "parserOpts": {
    "parser": "recast"
  },
  "generatorOpts": {
    "generator": "recast"
  }
}

You will also need to install recast to make this work:

npm install recast

To run the transform on your sources (src/) and output them to build/, run

node_modules/.bin/babel --out-dir build src

To build your project, create a simple build script (e.g. build.js) like this:

const Compiler = require('google-closure-compiler').compiler;

const compiler = new Compiler({
  js: [
    'build/**.js',
    // add directories for your dependencies, if any, here
  ],
  entry_point: 'build/index.js',
  module_resolution: 'NODE',
  dependency_mode: 'STRICT',
  process_common_js_modules: true,
  jscomp_error: ['newCheckTypes'],
  // Uncomment and modify for dependencies without Closure annotations
  //hide_warnings_for: ['node_modules']
  js_output_file: 'bundle.js'
});

compiler.run((exit, out, err) => {
  if (exit) {
    process.stderr.write(err, () => process.exit(exit));
  } else {
    process.stderr.write(out);
    process.stderr.write(err);
  }
});

To run the Compiler, simply call

node build.js

What the plugin does

Convert module namepaths to imported types

Closure Compiler does not allow JSDoc's namepaths with module identifiers as types. Instead, with module_resolution: 'NODE', it recognizes types that are imported from other files. Let's say you have a file foo/Bar.js with the following:

/** @module foo/Bar */

/**
 * @constructor
 * @param {string} name Name.
 */
const Bar = function(name) {
  this.name = name;
};
export default Bar;

Then you can use the Bar type in another module with

/**
 * @param {module:foo/Bar} bar Bar.
 */
function foo(bar) {}

This is fine for JSDoc, and this plugin transforms it to something like

/**
 * @param {foo$Bar} bar Bar.
 */
function foo(bar) {}
const foo$Bar = require('./foo/Bar');

With this, the type definition is recognized by Closure Compiler.

Convert JSDoc typedefs to Closure typedefs

JSDoc uses a nice, documentable format for {Object} typedefs:

/**
 * @typedef {Object} Foo
 * @property {string} bar Bar.
 * @property {module:types.Baz} baz Baz.
 */

Such typedefs are not understood by Closure compiler, so they are transformed to something like

/**
 * @typedef {{bar: (string), baz: (_types_Baz)}}
 */
export let Foo;

Properties marked as optional with JSDoc notation are also handled. The plugin will transforms @property {number} [foo] Foo. or @property {number=} foo Foo. to foo: (undefined|number).

Notes

To avoid the need for source maps, line numbers are retained by this plugin. This is the reason why the require() assignments are added at the bottom of each file.