Proposal for exact matching and matching at a position in RegExp

Steve L. steves_list at
Tue Feb 9 23:46:06 PST 2010

>> Basically the proposal is to add parameters which can override the
>> internal state of the RegExp.
> Does anyone have any comments on this?
> Can I put it in a place where it will be considered for the next
> ECMAScript?  The overall idea seems relatively uncontroversial since
> it was already implemented by Mozilla (for the exact same reason).  I
> have proposed a specific API enhancement too.

I do not believe it was implemented for "the exact same reason." It seems 
you are merely looking for a way to match exactly at a given character 
position, and you correctly note that /y is not an elegant solution for this 
problem. However, although /y can be used to solve this problem, my 
understanding is that it was designed to work similarly to the \G regex 
token from Perl/PCRE/Java/.NET/etc. while tying in nicely with the lastIndex 
property. An important feature of /y (and \G from other regex flavors) is 
that, with global regexes (compiled with /g), each successive match must 
start where the last match ended. This is a very useful feature for writing 
some types of simple parsers, etc.  And in the process of smartly solving 
this problem, you get an inelegant solution to your problem as a side 
effect, free of charge.

Steven Levithan

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