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JavaScript Patterns 5.6 Static Members

2024-07-10 08:14:42   219人阅读

Public Static Members

// constructorvar Gadget = function (price) {    this.price = price;};// a static methodGadget.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 prototypeGadget.prototype.setPrice = function (price) {    this.price = price;};// a normal method added to the prototypeGadget.prototype.isShiny = function () {    return Gadget.isShiny.call(this);};// Attempting to call an instance method statically won’t worktypeof 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

// constructorvar 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 immediatelyvar iphone = new Gadget();iphone.getLastId(); // 1var ipod = new Gadget();ipod.getLastId(); // 2var ipad = new Gadget();ipad.getLastId(); // 3

References: 

JavaScript Patterns - by Stoyan Stefanov (O`Reilly)


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