adambabik / es6-comprehensions

Array comprehensions compiled to ES5.

es6-comprehensions

Compiles JavaScript array comprehensions (proposed in ES6) to ES5-compatible syntax. For instance:

var squared = [ for (x of [1,2,3,4,5]) if (x > 2) x * x ];

compiles to:

var $__getIterator = function(iterable) { ... };
var $__arrayIterator = function(array) { ... };

var squared = function() {
  var $__result = [];

  for (var $__0 = $__getIterator([1,2,3,4,5]), $__1; !($__1 = $__0.next()).done; ) {
    var x = $__1.value;

    if (x > 2) {
      $__result.push(x * x);
    }
  }

  return $__result;
}.bind(this)();

I'm glad to inform you that es6-comprehensions is now a part of es-next project.

For more information check out the current draft for ECMAScript 6.

Please notice that the syntax has changed and many resources is still using the old one.

Installation

$ npm install es6-comprehensions [--save]

Support

Array comprehensions progressed to the Draft ECMAScript 6 Specification. It doesn't mean that there will be no changes or that array comprehensions will be included in the final ES6 Specification.

ES6 defines also iterators that can be used together with for-of loops that can be used in array comprehensions. This translator does not support iterators in for-of loops. It translates for-of loops to plain for loops. Thus, it supports only plain JS arrays.

Todo

• Consider replacing plain for loop with forEach method. It will result in more compact code, Invalid as for..of support was added in version 0.3.0.
• Consider migration to escodegen. Removed in order to follow up esnext's dependencies.

Development

1. Clone the repository.
2. Run npm install.
3. Do your changes.

Pull requests are highly appreciated.

Changelog

v0.3.1

• Switched to esprima-fb.

v0.3.0

• Added support for for..of loop. (Thanks @vslinko for PR.) Important! Generated code contains two more necessary functions.

v0.2.3

• Binding current scope to the generated function expression. This allows one to use this in an array comprehension. An example can be found in a test file. (Thanks @vslinko for PR.)

v0.2.2

• Using ast-util to generate safe temporary variables.

v0.2.1

• Replaced ComprehensionExpression with CallExpression instead of ExpressionStatement.

v0.2.0

• Changed API to conform to esnext's requirements.

License

BSD

es6-comprehensions's Issues

Forward this to call expressions

I want to make:

[for (option of options) this.renderOption(option)]

Your comprehensions doesn't support for-of over iterable

You can use https://github.com/vslinko/es6-for-of to support comprehensions over iterable.

Make compatible with esnext?

I'd love to use this project as part of esnext, but it looks like the API isn't the same. I wanted to check with you to see if you'd be willing to change the API of this project to the API used by the other projects used by esnext. That is, the main module should export two methods:

• transform(object): object: takes an Esprima AST and returns a modified AST that replaces, in this project's case, ComprehensionExpression nodes with the equivalent ES5
• compile(string): { code: string, map: object }: this method compiles the given source code by parsing it into an AST, passing the AST to transform, and using recast.print() to get both the code and the source map

You currently have a transform method, but it's closer to my compile method. And parse is similar to my transform method except that it takes source code as input instead of an AST.

Let me know if you'd be willing to discuss this API change!

Syntax is out of date

Draft spec has newer syntax, e.g.

[  for (x of [1,2,3,4,5]) square(x) ]

instead of the obsolete

[ square(x) for (x of [1,2,3,4,5]) ]