JavaScript Patterns 5.6 Static Members

浏览数：27 / 时间：2015年06月08日

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