Public Static Members
// constructor var Gadget = function (price) { this.price = price; }; // a static method Gadget.isShiny = function () { // this always works var msg = "you bet"; // Checking if the static method is called by instance. if (this instanceof Gadget) { // this only works if called non-statically msg += ", it costs $" + this.price + ‘!‘; } return msg; }; // a normal method added to the prototype Gadget.prototype.setPrice = function (price) { this.price = price; }; // a normal method added to the prototype Gadget.prototype.isShiny = function () { return Gadget.isShiny.call(this); }; // Attempting to call an instance method statically won’t work typeof Gadget.setPrice; // "undefined"
Testing a static method call:
Gadget.isShiny(); // "you bet"
Testing an instance, nonstatic call:
var a = new Gadget(‘499.99‘); a.isShiny(); // "you bet, it costs $499.99!"
Private Static Members
• Shared by all the objects created with the same constructor function
• Not accessible outside the constructor
// constructor var Gadget = (function () { // static variable/property var counter = 0, NewGadget; // this will become the new constructor implementation NewGadget = function () { counter += 1; }; // a privileged method NewGadget.prototype.getLastId = function () { return counter; }; // overwrite the constructor return NewGadget; }()); // execute immediately var iphone = new Gadget(); iphone.getLastId(); // 1 var ipod = new Gadget(); ipod.getLastId(); // 2 var ipad = new Gadget(); ipad.getLastId(); // 3
References:
JavaScript Patterns - by Stoyan Stefanov (O`Reilly)