I'm running the following code on Webkit:

var scriptElements = document.scripts;

var scriptUrls = [];

// URL matching

var regexp = /b((?:[a-z][w-]+:(?:/{1,3}|[a-z0-9%])|wwwd{0,3}[.]|[a-z0-9.-]+[.][a-z]{2,4}/)(?:[^s()<>]+|(([^s()<>]+|(([^s()<>]+)))*))+(?:(([^s()<>]+|(([^s()<>]+)))*)|[^s`!()[]{};:'.,<>?«»“”‘’]))/i;

for (var i = 0; i < scriptElements.length; i++) {

    element = scriptElements[i];

    var urls = element.innerHTML.match(regexp);

    console.log('local', urls);

    scriptUrls.concat(urls);

    console.log('global', scriptUrls);

}

I see non-empty arrays printed after 'local' but the 'global' always stays as an empty array. What's going on?