Today I came across a very strange JavaScript regular expression issue. When using the global modifier (//g), RegExp.test() yields different values in subsequent calls. Can anyone explain why?

var s = "youtube.com/watch?v=XyeebVA3DNk";

var re1 = /^youtube\.com\/watch[a-zA-Z0-9_\-\?\&\=\/]+/g;

console.log(re1.test(s)); // true
console.log(re1.test(s)); // false
console.log(re1.test(s)); // true
console.log(re1.test(s)); // false
console.log(re1.test(s)); // true
console.log(re1.test(s)); // false
console.log(re1.test(s)); // true

var re2 = /^youtube\.com\/watch[a-zA-Z0-9_\-\?\&\=\/]+/;

console.log(re2.test(s)); // true
console.log(re2.test(s)); // true
console.log(re2.test(s)); // true
console.log(re2.test(s)); // true
console.log(re2.test(s)); // true
console.log(re2.test(s)); // true

I am able to reproduce this in Chrome 8 and FireFox 3.6.

javascript regex
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