Bug 26911 – $0 backreference no longer working

• Component: JavaScriptCore
• Status: RESOLVED INVALID

[Johan Attali]

The $0 backreference in the replace function is no longer working and gives an undefined value even if the pattern matched.

ex. "1T2".replace(/\w+/g, '<a href="http://$0">$0</a>'); is not working
while "1T2".replace(/(\w+)/g, '<a href="http://$1">$1</a>'); is working.

The object RegExp.$0 is to be set to undefined whatever the pattern matchin was.

[Keishi Hattori]

Is this true?  
ECMA 262 says that $n is the nth capture where n is a single digit 1-9.
ECMAScript5 Draft says the same. The matched substring is $&.

[Johan Attali]

I just tried $& and it is indeed working. 
Though you are absolutely right (the specs only specify that digits 1-9 to be used) you might want to keep $0 for backward compatibility, which is actually why I found and filed this bug.

(In reply to comment #1)
> Is this true?  
> ECMA 262 says that $n is the nth capture where n is a single digit 1-9.
> ECMAScript5 Draft says the same. The matched substring is $&.

[Keishi Hattori]

I think Firefox nor Opera supports this. I don't think we'll want to implement new syntax which encourages incompatible JS.

[Alexey Proskuryakov]

Given the information above, this is an improvement in behavior.

Are there any (many?) live sites affected by this change? Does IE support this syntax? Please feel free to re-open this bug for further consideration if so.

[Johan Attali]

Well tested on IE 6, $0 is also not working either (while is $& is)...
Now I'm wondering how $0 managed to become popular ??
(In reply to comment #4)
> Given the information above, this is an improvement in behavior.
> 
> Are there any (many?) live sites affected by this change? Does IE support this
> syntax? Please feel free to re-open this bug for further consideration if so.