regular expression for equal number of two chars

[programAngel]

how can I write regular expression that accept any string that has equal number of 'a' and 'b'?

[mrhoo]

It is easy with 2 expressions-

var equalAandB=(str.match(/a/g) || []).length === (str.match(/b/g) || []).length;

[007Julien]

it's too easy to build a function with a variant...

String.prototype.asMuchAs=function(a,b){return this.replace(new RegExp(a,'ig'),'').length==this.replace(new RegExp(b,"ig"),'').length}
// Test
var str="NATO Apologizes for Deaths in Airstrike, Explosion Hits Police Bus in Pakistan, Cameron to Appear at Hacking Inquiry".split(',');
for (var i in str) alert(str[i]+' '+str[i].asMuchAs('a','i'));