ES6 feature: Update to ES6 identifier grammar

[mathiasbynens]

Esprima currently implements ES5 identifier grammar. It would be nice to update to ES6.

In case it’s helpful — I just wrote a blog post that documents the differences between ES5 and ES6 identifiers, with examples: https://mathiasbynens.be/notes/javascript-identifiers-es6

[ikarienator]

@mathiasbynens You might be interested in this as well https://bugs.ecmascript.org/show_bug.cgi?id=4097#c4

[mathiasbynens]

@ikarienator Thanks for the heads up! Is this observable? If so, how?

E.g. how should the following code behave:

Function('var var;'); // grammar error → throws?
Function('var v\\u0061r;'); // early error → throws (before execution)?

[michaelficarra]

@mathiasbynens They should both throw. I can't think of any way someone would be able to distinguish an early error from a grammar error.

[ariya]

Since this is quite a big topic, I'll spawn few new tickets which will tackle the individual issues separately.

[ariya]

This is now covered by all the most recent commits.