Using Regular Expressions (JavaScript 1.2/JScript 4+)

String.prototype.LTrim=new Function("return this.replace(/^\\s+/,'')")
String.prototype.RTrim=new Function("return this.replace(/\\s+$/,'')")
String.prototype.Trim=new Function("return this.replace(/^\\s+|\\s+$/g,'')")

or

function LTrim(str) { 
   for (var k=0; k<str.length && str.charAt(k)<=" " ; k++) ;
   return str.substring(k,str.length);
}
function RTrim(str) {
   for (var j=str.length-1; j&gt;=0 && str.charAt(j)<=" " ; j--) ;
   return str.substring(0,j+1);
}
function Trim(str) {
   return LTrim(RTrim(str));
}