Consider adding an ES5 identifier test about compat-table HOT 7 CLOSED

Are U+200C and U+200D (from all the allowed characters) the only ones that fail in some clients at the moment?

from compat-table.

Not significant, but maybe:

var supportsZeroWidth = (function() {
  try {
    return eval('_\u200c\u200d = true');
  } catch(e) { }
}());

from compat-table.

U+200C and U+200D are the only two characters that haven’t changed categories since Unicode 3.0 yet still fail in multiple browsers, even though they’re explicitly mentioned in the spec. (Btw, I fixed the U+200C/U+200D bugs in V8 and WebKit/JavaScriptCore now.)

It’s funny, really; most browsers that claimed full ES5-compliance months ago still fail on a simple var a\u200c\u200d — only stable versions of IE9 and Firefox 10 get it right.

Other than those characters, the spec mentions the Unicode categories that are allowed in IdentifierStart and IdentifierPart — but that’s a separate issue. Of course, not all JavaScript engines have the same level of Unicode support yet. As the spec says:

ECMAScript implementations may recognize identifier characters defined in later editions of the Unicode Standard. If portability is a concern, programmers should only employ identifier characters defined in Unicode 3.0.

So no, there are lots of other identifiers that fail in multiple browsers at the moment, but these are one of the few characters that are explicitly mentioned in the ES5 spec (not deferred to a Unicode spec) yet they still fail. See the list of links to browser bugs in my post — only Firefox nightly seems to have full Unicode 6.1.0 support.

Nice simplification of the feature test!

from compat-table.

I see... So if we only consider Unicode 3.0, do implementations fare well with all the allowed characters?

from compat-table.

Other than the ZWJ and ZWNJ characters, I haven’t found a problem with non-Unicode 3.0 chars in any browser. As I tested some seriously crazy symbols, I doubt there are any. (I mostly tested browser implementations, though.)

The variable name validator might be useful when testing this further, as it will show a warning if a given identifier would not be allowed if the Unicode 3 database would’ve been used instead of the Unicode 6.1 database. E.g. http://mothereff.in/js-variables#%5Cu0cf1

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Yeah. I'm surprised test262 didn't catch that. Need to check if they test for it.

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Added. Thanks.

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