function test() {
var a='';
for (var i=0; i<100; i++) {
a+='abcdefghij';
}
a+='k';
var before = new Date();
var loops = 40000;
for (var i=0; i<loops; i++) {
a.indexOf('k');
}
var after = new Date();
time = after-before;
result(time);
}

Time: