es6-module-transpiler-amd-formatter

ES6 Module Transpiler Formatter to Output AMD define() Format.

This is a fork of the original project with the following improvements:

• Optional disabling of named modules generation.
• Optimized code generation if a module has only one export.
• Default export optimization for project, which mix ES6 and AMD.JS modules.
• Up-to-date NPM module dependencies, including static code cheks and test code coverage.

Overview

ES6 Module Transpiler es6-module-transpiler is an experimental compiler that allows you to write your JavaScript using a subset of the current ES6 module syntax, and compile it into various formats. The es6-module-transpiler-amd-formatter is one of those output formats that is focus on enabling the use of ES6 modules thru RequireJS today.

Disclaimer

This output format compromises in few of the ES6 features in ES6 modules, including live bindings, sealed objects, etc. This compromise is Ok when you try to use them as AMD modules.

Usage

Build tools

Since this formatters is an plugin for es6-module-transpiler, you can use it with any existing build tool that supports es6-module-transpiler as the underlaying engine to transpile the ES6 modules.

You just need to make sure that es6-module-transpiler-amd-formatter is accessible for those tools, and pass the proper formatter option thru the es6-module-transpiler configuration.

Executable

If you plan to use the compile-module CLI, the formatters can be used directly from the command line:

$ npm install es6-module-transpiler
$ npm install es6-module-transpiler-amd-formatter
$ ./node_modules/.bin/compile-modules convert -f es6-module-transpiler-amd-formatter path/to/**/*.js -o build/

The -f option allow you to specify the path to the specific formatter, which is this case is an installed module called es6-module-transpiler-amd-formatter.

Library

You can also use the formatter with the transpiler as a library:

var transpiler = require('es6-module-transpiler');
var AMDFormatter = require('es6-module-transpiler-amd-formatter');
var Container = transpiler.Container;
var FileResolver = transpiler.FileResolver;

var container = new Container({
  resolvers: [new FileResolver(['lib/'])],
  formatter: new AMDFormatter()
});

container.getModule('index');
container.write('out/mylib.js');

Named Modules

Named modules will be produced by default. If you want to process the modules by the RequireJS optimizer and let the r.js assign the module names, you can configure this formatter to produce unnamed modules.

If you use the command-line tool, set the environment variable AMDFORMATTER_NAMED_MODULES to false:

AMDFORMATTER_NAMED_MODULES=false ./node_modules/.bin/compile-modules ...

If you use the library, set the option namedModules to false in the constructor of the formatter:

var container = new Container({
  resolvers: [new FileResolver(['lib/'])],
  formatter: new AMDFormatter({ namedModules: false })
});

Simplified Exports

If you maintain a large project compiled by an AMD.JS bundler, you may be looking for a way of supplying modern ES6 modules, but you will not be able to replace the bundler because of its additional functionality (RequireJS) and the existing code base. ES6 and AMD.JS are not entirely compatible, especially when dealing with the default exports. The following rules allow to mix ES6 and AMD.JS modules in a single build:

• Default exports allowed only at the end of a module to allow exporting them by return and not by the wrapper exports object with the default key.
• A default export imported directly, without the wrapper object with the default key.
• Named exports imported as an object, with the exported names as keys.

Depending on those rules, the following ES6 module:

import assert from "./assert";

export default function (a, b) {
  assert(a);
  assert(b);
  return a + b;
};

will be transpiled as if it was coded as a native AMD.JS:

define("component/foo", ["./assert"], function (assert) {
  "use strict";

  return function (a, b) {
    assert(a);
    assert(b);
    return a + b;
  };
});

ES6 modules developed for an AMD.JS project this way will be reusable in the future, when the bundler will be replaced.

If you use the command-line tool, set the environment variable AMDFORMATTER_DIRECT_EXPORTS to true:

AMDFORMATTER_DIRECT_EXPORTS=true ./node_modules/.bin/compile-modules ...

If you use the library, set the option directExports to true in the constructor of the formatter:

var container = new Container({
  resolvers: [new FileResolver(['lib/'])],
  formatter: new AMDFormatter({ directExports: true })
});

You will want to disable the named modules generation, if you combine ES6 and AMD.JS modules in a single (build) project and want to let the RequireJS optimizer (r.js) to generate the module names.

Supported ES6 Module Syntax

Again, this syntax is in flux and is closely tracking the module work being done by TC39. This package relies on the syntax supported by es6-module-transpiler, which relies on esprima, you can have more information about the supported syntax here: https://github.com/square/es6-module-transpiler#supported-es6-module-syntax

Compiled Output

First of all, the output format for define() might looks alien even for many developers, but considering that es6-module-transpiler relies on Recast to mutate the original ES6 code, it can output the corresponding sourceMap, you should be able to debug the module code without having to understand the actual output format.

Default export

For a module without imports, and a single default exports:

export default function (a, b) {
  return a + b;
}

will produce something like this:

define("component/foo", ["exports"], function(__exports__) {
  "use strict";

  function __es6_export__(name, value) {
    __exports__[name] = value;
  }

  __es6_export__("default", function(a, b) {
    return a + b;
  });
});

Imports and exports

A more complex example will look like this:

import assert from "./assert";

export default function (a, b) {
  assert(a);
  assert(b);
  return a + b;
};

and the output will be:

define("component/foo", ["./assert", "exports"], function(component$assert$$, __exports__) {
  "use strict";

  function __es6_export__(name, value) {
    __exports__[name] = value;
  }

  var assert = component$assert$$["default"];
  __es6_export__("assert", component$assert$$["assert"]);

  __es6_export__("default", function(a, b) {
    assert(a);
    assert(b);
    return a + b;
  });
});

Part of the goal, is try to preserve as much as possible the original code of the module within the factory function. Obviously, this is difficult when you have to export default functions and other declarations. The only modifications you will see in the body are the calls to the __es6_export__() method to export the new value when defined or updated, the rest of the code will remain immutable.

Default export optimisation

If the default export is the single export in a module and it is not the last statement, the __es6_export__ function will not be generated. For example:

export default function (a, b) {
  return a + b;
}
console.log('done');

will produce something like this:

define("component/foo", ["exports"], function(__exports__) {
  "use strict";

  __exports__["default"] = function(a, b) {
    return a + b;
  };
  console.log('done');
});

If the default export is the single export in a module and it is the last statement, it will be returned from the module withotu using the __exports__ parameter. For example:

export default function (a, b) {
  return a + b;
}

will produce something like this:

define("component/foo", [], function() {
  "use strict";

  return function(a, b) {
    return a + b;
  };
});

Contributing

1. Fork it
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create new Pull Request

Thanks, and enjoy living in the ES6 future!