Add ECMAScript 6 features

[nzakas]

This is a rollup that will let us keep track of ES6 progress.

• let declarations
• const declarations
• Regular expression u flag
• Regular expression y flag
• Binary literals
• New octal literals
• Arrow functions
• Default parameters
• Rest parameters
• Spread operator
• super references
• Classes
• for-of loops
• Generators
• Object literal property shorthand
• Object literal method shorthand
• Object literal computed properties
• Template strings
• Destructuring
• Unicode code point escapes
• Allow duplicate object literal properties (except __proto__)
• Modules

[nzakas]

The let and const changes are in. Next up: regular expression flags.

[nzakas]

In order to make the regular expression flags work, I needed to add a regex property to both AST nodes and literal nodes to coincide with Esprima Harmony. I've got this working, but need to update the AST tests for the various third-party libraries that Esprima uses to validate AST output.

[FredKSchott]

@nzakas which of these would you reccomend to get started on?

[nzakas]

I think allowing duplicate properties in strict mode is the easiest to get started with. I'd call that objectLiteralDuplicateProperties.

After that, Unicode code point escapes (see https://leanpub.com/understandinges6/read#leanpub-auto-better-unicode-support)

[nzakas]

I'm currently working on generators.

[FredKSchott]

I'm starting work on Unicode code point escapes

[nzakas]

Generators and code point escapes have been merged in.

[nzakas]

Next priority is template literals. @FredKSchott interested in taking that?

[FredKSchott]

definitely, I'll tackle that next (away for the long weekend but I'll take a look next week)

They're supported in V8 now, right? Makes sense to do them next

[nzakas]

Yup! And also in io.js now.

I'm planning on attacking arrow functions when I have some energy.

[xjamundx]

Interested in taking a shot in default params, though I'm not sure how much work it will be/take I'll have...

[FredKSchott]

Template strings are done! I'd be interested in taking on destructuring or rest parameters next. @nzakas thoughts?

[xjamundx]

+1 for destructuring.

[FredKSchott]

@xjamundx whoops, just saw your post above on taking rest params. Are you still planning on working on that? nvm, I forgot that Rest params != Default params

[nzakas]

Rest params are much easier. Destructuring is tricky. You can decide the level of challenge you want. :)

[FredKSchott]

[nzakas]

👍

[trusktr]

👍 for modules and classes!

[AbrahamAlcaina]

+1 classes

[FredKSchott]

Quick update: I've been completely swamped this week, and haven't been able to work on this at all this week. I probably won't be free again for another week or two. Anyone who wants to grab rest params or destructuring should feel free.

[koistya]

👍

[nzakas]

Thanks for the update, Fred.

[nzakas]

Tackling super references now.

[gaearon]

👍 to destructuring and arrow functions

[xjamundx]

I have like 45 minutes to takea stab at either. I'll try arrow functions.

[nzakas]

I'd be super impressed if you could do arrow functions in 45 minutes, it's a bit complicated because you don't know that an expression is the beginning of an arrow function until the => is encountered.

If you want a nice simple one, rest parameters would probably work.

[xjamundx]

Yeah def won't be done in 45, but I think in a few hours I could get this to work. Will open PR shortly... it's coming along. A lot of the core stuff was already ported over for other ES6 stuff...

[xjamundx]

Will take a stab at destructuring. Hoping to have a PR with just some broken tests today, but imagine it will take a few weeks to track down every last piece.

[FredKSchott]

👍

[xjamundx]

Hey people this is pretty great. 4 things left!

[gaearon]

<3

[xjamundx]

✋ for rest next

[endel]

facebook/esprima supports classes.

[nzakas]

Esprima classes support: jquery/esprima#1061

[xjamundx]

Well that makes things easier :)

[nzakas]

Working on classes now.

[xjamundx]

👏

[FredKSchott]

you guys are killing it 👏 👏 👏

[nzakas]

Ran into a bit of trouble with classes. The Harmony branch is different that Esprima's master now (master being the most correct). Will probably take me a bit to work through it unless someone else wants to give it a shot.

[xjamundx]

I'm still trying to grok the destructuring defaults spec. Once I'm done with that I'll try to throw my hat into either classes or modules. Whatever's left....

[niels4]

Fast work on getting these es6 features implemented!

I noticed an issue with rest parameters though, they don't seem to get added to the scope's variable list. I noticed this when trying to use eslint to validate a function with rest parameters.

var func = function (first, ...rest) {
  return rest;
};

I am getting a 'rest' is not defined (no-undef) error. The underlying cause seems to be that when the rule's function looks at context.getScope().variables, a variable named 'rest' is not in the list.

see eslint/eslint#1870 to fully replicate

[xjamundx]

Cool just saw eslint/eslint#1870.

[nzakas]

As I mentioned there, this is an issue with escope, not espree.

[nzakas]

Don't look now, modules is the last feature!

[xjamundx]

This is great news!! Well done!

[fczuardi]

should we file a separate bug just for the modules support?

In this related bug I posted an example of how espree differs from esprima when used with escope eslint/eslint#1978 (comment)

[nzakas]

Modules are already properly supported.