if (!num.toFixed) 
{

 Number.prototype.toFixed = function(precision) {
     var power = Math.pow(10, precision || 0);
     return String(Math.round(this * power)/power);
 }

}

// OR

  Number.prototype.toFixed = function(precision) 
  {
     var num = (Math.round(this*Math.pow(10,precision))).toString();
     return num.substring(0,num.length-precision) + "." + 
            num.substring(num.length-precision, num.length);
  }