This is THE fastest way and the most secure to test a string being a number.
I've also tried using Regex which worked ok (~800ms i recall)
var s = ["123e6","not num", "not num"];
P = 100000;
y = 0;
d = new Date();
do{
if( !isNaN(s[P%3]) )
y++;
}while(--P);
console.log( (new Date()).getTime() - d.getTime() )
it only takes about 515ms which is very fast on avarage!
Together with the new int/float regex: /(([-]|\b)\d+\.?\d*|[-]?\.\d+)(e[-]?\d+|\b)/gi its working really good !!
I've improved the jsParser speed from 6.8ms to 5.3ms !!