Subj : lastIndex property of newly created RegExp object
To   : netscape.public.mozilla.jseng
From : Martin Honnen
Date : Mon Nov 29 2004 07:01 pm

I have run into what I believe to be a bug with the lastIndex property 
of a newly created RegExp object when looking at the ECMAScript edition 
3 specification but as both Spidermonkey (tested with xpcshell of 
Mozilla 1.7.3) and Rhino (tested with Rhino shell of 1.5R5) behave the 
same I am a bit puzzled and thought I ask here what others think.

Test case looks as follows:

function findLine (text) {
   var linePattern = /.*(\r\n|\r|\n)/g;
   output('linePattern.lastIndex before exec: ' + linePattern.lastIndex);
   var match = linePattern.exec(text);
   output('match: ' + match);
}

function output (text) {
   if (typeof document != 'undefined' && document.write) {
     document.write('<p>' + text + '</p>\r\n');
   }
   else if (typeof print != 'undefined') {
     print(text);
   }
}

function test () {
   var text = 'Line 1\r\nLine 2\r\nLine 3\r\nLine 4';
   for (var i = 0; i < 4; i++) {
     findLine(text);
   }
}

test();


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."
so I expect the lastIndex of that linePattern to be 0 on each call of 
the function findLine but somehow the lastIndex is stored between 
function calls so Rhino or Spidermonkey output the following:

Rhino 1.5 release 5 2004 03 25
js> load('test2004112901.js')
linePattern.lastIndex before exec: 0
match: Line 1
,

linePattern.lastIndex before exec: 8
match: Line 2
,

linePattern.lastIndex before exec: 16
match: Line 3
,

linePattern.lastIndex before exec: 24
match: null


When I run the example as uploaded here
http://home.arcor.de/martin.honnen/mozillaBugs/ecmascript/test2004112902.html
with MSIE 6 it always shows 0 for the lastIndex.

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

-- 

	Martin Honnen
	http://JavaScript.FAQTs.com/

.