Rubular versus javascript regexp capture groups

Noticed a difference between what Rubular.com and Javascript regexes:

'catdogdogcatdog'.match(/cat(dog)/g);  // JS returns ['catdog', 'catdog']  

I expected to captu开发者_如何学JAVAre 'dog' twice but instead I get 'catdog' twice.

Rubular captures 'dog' twice as expected: http://rubular.com/r/o7NkBnNs63

What is going on here exactly?

No, Rubular also matches catdog twice. It also shows you the contents of the capturing group, which captured dog twice.

You want something like this:

var myregexp = /cat(dog)/g;
var match = myregexp.exec(subject);
while (match != null) {
    dog = match[1]
    // do something, Gromit!
    match = myregexp.exec(subject);
}