Subj : Re: lastIndex property of newly created RegExp object
To   : Martin.Honnen
From : Brendan Eich
Date : Mon Nov 29 2004 11:33 am

Martin Honnen wrote:

> Now section 15.10.4.1 of ECMA says that for a newly created RegExp object
>   "The lastIndex property of the newly constructed object is set to 0."


See 7.8.5 Regular Expression Literals:

A regular expression literal is an input element that is converted to a 
RegExp object (section 15.10) when it is scanned. The object is created 
before evaluation of the containing program or function begins. 
Evaluation of the literal produces a reference to that object; it does 
not create a new object. Two regular expression literals in a program 
evaluate to regular expression objects that never compare as === to each 
other even if the two literals' contents are identical. A RegExp object 
may also be created at runtime by new RegExp (section 15.10.4) or 
calling the RegExp constructor as a function (section 15.10.3).


So the SpiderMonkey and Rhino engines create one RegExp object for each 
source Regular Expression Literal, before evaluation of the containing 
program or function begins (i.e., "when [the literal] is scanned").


> with MSIE 6 it always shows 0 for the lastIndex.


Another MS JScript bug.


> Any thoughts on why Spidermonkey and Rhino somewhere store and restore 
> the lastIndex property between function calls?


They follow the spec.  There is no new regexp per call, only one per 
literal scanned.

/be

.