<!DOCTYPE>
<html>
<head>
<title></title>
</head>
<body>
</body>
</html>
<script type="text/javascript">
var t1 = new Date().getTime();
var string = '';
for(i=1; i<=500000; i++){
string += i;
}
var t2 = new Date().getTime();
console.log(t2-t1);
var arr = [];
for(i=1; i<=500000; i++){
arr[i] = i;
}
var t3 = new Date().getTime();
arr.join();
var t4 = new Date().getTime();
console.log(t4-t3);
</script>Conclusion
Chrome += is faster than arr.join() while IE and Firefox arr.join() is faster than +=
Chrome += is about 8 times faster than arr.join()
IE: arr.join() is 3 times faster than +=
Firefox: arr.join() is 3 times faster than += Firefox
is 10 times faster than IE
Most people use a little more IE, so in js projects, js processing strings using arr.join will be better than +=