Checks If String Contains Only White Spaces

String.prototype.isEmpty.js

/*
 *  Checks If String Contains Only White Spaces
 * 
 *  Useful for Fields Validation $input.val().isEmpty()
 */
String.prototype.isEmpty = function () {
  return /^\s*$/.test(this);
}

Creating regexp for each function call isn't super efficient. This would be faster:

String.prototype.isEmpty = (function(){
    var r = /^\s*$/;
    return function () {
        return r.test(this);
    }
})();