Trimming with Javascript

I simple but effective implementation of javascript for trimming extra spaces from a string. A good use of it could be on form validation.
The custom trim function :

function trim (str) {
var str = str.replace(/^\s\s*/, ''),
ws = /\s/,
i = str.length;
while (ws.test(str.charAt(--i)));
return str.slice(0, i + 1);
}

Typical use of trim :

function validate()
{
val = document.getElementById("txt").value;
retval = trim12(val);
alert(retval);

}

Surely if you use any rich javascript library a trim method should come with it. Have fun :)