regex test problem

[BubikolRamios]

How do you explain that ?

regexPattern = new RegExp("a","gi");
s = "a";
        alert (regexPattern.test(s));//--> true
        alert (regexPattern.test(s));//--> false
        alert (regexPattern.test(s));//--> true
        alert (regexPattern.test(s));//--> false
        //......

EDIT: if I modify each alert:

 alert (regexPattern.test(s) + s.match(regexPattern));

obviously result of

 s.match(regexPattern)

is the same on each alert.

[Philip M]

Hmm. Very odd! You seem to have exposed a bug (not a flower! ) in the Javascript regex engine. Same in IE and Chrome.

var s = "a";
alert (/a/gi.test(s)); // true
alert (/a/gi.test(s)); // true
alert (/a/gi.test(s)); // true
alert (/a/gi.test(s)); // true

"If you make it idiot proof, they'll build a better idiot"

[BubikolRamios]

Found a flower or bug

Bugs also there (-:

Yeah, tested the thing in chrome, before submiting here.
Not to mention hours lost, before 'lamp' turned on: "Damn, there something smell bad about .test".
I had .test in a loop and "a" string has been changing and on every second loop bad result.

[AndrewGSW]

As with exec (or in combination with it), test called multiple times on the same global regular expression instance will advance past the previous match.

Mozilla

regexPattern = new RegExp("a","gi");
s = "a";
        alert (regexPattern.test(s));//--> true
        alert(regexPattern.lastIndex); // 1
        alert (regexPattern.test(s));//--> false
        alert(regexPattern.lastIndex); // 0
        alert (regexPattern.test(s));//--> true
        alert(regexPattern.lastIndex); // 1
        alert (regexPattern.test(s));//--> false
        alert(regexPattern.lastIndex); // 0

[AndrewGSW]

If you remove the "g" global modifier - which is not relevant to test() - then it behaves as expected.

Added: I won't have JavaScript besmirched
(only joshing!)

[Philip M]

Originally Posted by AndrewGSW

If you remove the "g" global modifier - which is not relevant to test() - then it behaves as expected.

You are right! Woot!
We learn something every day. Sometimes something worth knowing!

[007julien]

It is the same thing with prompt or confirm and if an "a" take place of s !

In short (See this MDN page *) you have to restore the regexPattern.lastIndex to 0 before each new test !

Good to know. Thanks !

(*) Or better ECMAScript Language Specification 15.10.6.2 and 15.10.6.3