Here you can find the source of isEmpty()
String.prototype.isEmpty = function() { return this.trim() === ""; }
String.prototype.isEmpty = function() { return (!this || 0 === this.length); };
String.prototype.isEmpty = function() { return (this == ''); };
String.prototype.isEmpty = function () { "use strict"; return (this.length === 0 || !this.trim()); };
String.prototype.isEmpty=function(){ return this.trim()==""; };
String.prototype.isEmpty = function () { return (!this || this == "[object Null]" || this == "" || this == "undefined");
String.prototype.isEmpty = function(){ return (this === null || this === ''); };
String.prototype.isEmpty = function() { return (this.length === 0 || !this.trim()); Array.prototype.appendStringToElementAtIndex = function(index, str) { if(typeof this[index] === 'undefined' || typeof this[index] !== 'string') return false; this[index] += ' ' + str; };
String.prototype.isEmpty = function() { return (this.length === 0 || !this.trim()); };
String.prototype.isEmpty = function(){ if(typeof this !== 'string') { if(typeof this === 'object' && !(this instanceof String)){ throw { name: 'InvalidType', message: 'The current type is not a String' return this.length === 0; };