The javascript:

<code lang="JavaScript">
// the original code

Number.prototype.times = function(str){
var mainstr = "";
for(var i=0;i < this;i++){
mainstr += str;
}
return mainstr;
}

// tweaked

Number.prototype.Times = function(str){
for(var i=0;i < this;i++){
eval(str);
}
}
</code>

Usage:

<code lang="JavaScript">
var t = 4;
// using the original function
4.times("a"); // returns "aaa"
// using the tweaked version
4.Times("alert('a')"); // alerts 'a' 4 times
</code>