Strings that start with 0 are treated as octal numbers (base 8) in ECMAScript 3; however, this has changed in ES5. To avoid inconsistency and unexpected results, always specify the radix parameter: var month = "06", year = "09"; month…

Principle Make variables shouldn't be changed stand out using all caps. Add constants as static properties to the constructor function. // constructor var Widget = function () { // implementation... }; // constants Widget.MAX_HEIGHT = 320; Widget.MAX…

Function Application apply() takes two parameters: the first one is an object to bind to this inside of the function, the second is an array or arguments, which then becomes the array-like arguments object available inside the function. If the first…

Configuration Objects Passing a large number of parameters is not convenient. A better approach is to substitute all the parameters with only one and make it an object. var conf = { username: "batman", first: "Bruce", last: "Wayne…

Gets a length property containing the number of arguments the function expects: function func(a, b, c) {} console.log(func.length); var myFunc = function () { // serialize the arguments object as a JSON string and use that string as a key in your cac…

7.1 Singleton The idea of the singleton pattern is to have only one instance of a specific class. This means that the second time you use the same class to create a new object, you should get the same object that was created the first time. var obj =…

Scenario You want to use just the methods you like, without inheriting all the other methods that you’ll never need. This is possible with the borrowing methods pattern, which benefits from the function methods  call() and apply(). // call() example…

Loop through arguments and copy every property of every object passed to the function. And the result will be a new object that has the properties of all the source objects. function mix() { var arg, prop, child = {}; for (arg = 0; arg < arguments.le…

Shallow copy pattern function extend(parent, child) { var i; child = child || {}; for (i in parent) { if (parent.hasOwnProperty(i)) { child[i] = parent[i]; } } return child; } Deep copy pattern function extendDeep(parent, child) { var i, toStr = Obje…

No classes involved; Objects inherit from other objects. Use an empty temporary constructor function  F().  Set the prototype of  F() to be the parent object. Return a new instance of the temporary constructor. function Object(o) { function F() {} F.…