使用Object.create()进行JavaScript继承？

Question

我如何继承Object.create()？我试过这些,但都没有工作:

var B = function() {};
var A = function() {};
A = Object.create(B);
A.prototype.C = function() {};

和

var B = function() {};
var A = function() {};
A.prototype.C = function() {};
A = Object.create(B);

和

var B = function() {};
A = Object.create(B);
var A = function() {};
A.prototype.C = function() {};

没有任何效果.我该如何使用这个新的Object.create()函数？

Answer 1

在JavaScript中有几种继承方式

施工继承.如果您不需要调用超类型构造函数,请使用:

function Rectangle(length, width) { 
    this.length = length;
    this.width = width;
}

Rectangle.prototype.getArea = function() {
    return this.length * this.width;
};

// inherits from Rectangle
function Square(size) { 
    this.length = size;
    this.width = size;
}

Square.prototype = Object.create(Rectangle.prototype);

var rect = new Rectangle(6, 8);
var square = new Square(10);

console.log(rect.getArea());                // 48
console.log(square.getArea());              // 100
console.log(rect instanceof Rectangle);     // true
console.log(rect instanceof Object);        // true
console.log(square instanceof Square);      // true
console.log(square instanceof Rectangle);   // true
console.log(square instanceof Object);      // true

构造函数窃取.如果需要调用超类型构造函数,则使用:

function Rectangle(length, width) { 
    this.length = length;
    this.width = width;
}

Rectangle.prototype.getArea = function() {
    return this.length * this.width;
};

// inherits from Rectangle
function Square(size) { 
    Rectangle.call(this, size, size);
}

Square.prototype = Object.create(Rectangle.prototype);

var rect = new Rectangle(6, 8);
var square = new Square(10);

console.log(rect.getArea());                // 48
console.log(square.getArea());              // 100
console.log(rect instanceof Rectangle);     // true
console.log(rect instanceof Object);        // true
console.log(square instanceof Square);      // true
console.log(square instanceof Rectangle);   // true
console.log(square instanceof Object);      // true

Answer 2

Object.create()用于继承对象,而不是像你想要的那样构造.它几乎创建了一个新对象,旧对象设置为原型父对象.

var A = function() { };
A.prototype.x = 10;
A.prototype.say = function() { alert(this.x) };

var a = new A();
a.say(); //alerts 10

var b = Object.create(a);
b.say(); //alerts 10
b.x = 'hello';
b.say(); //alerts 'hello'

并且只是为了确保b不仅仅是a的克隆,

a.x = 'goodbye';
delete b.x;
b.say(); //alerts 'goodbye'

Answer 3

我用于此的模式是将每个类型包装在一个模块中,并公开create和prototype属性,如下所示:

var Vehicle = (function(){
        var exports = {};
        exports.prototype = {};
        exports.prototype.init = function() {
                this.mph = 5;
        };
        exports.prototype.go = function() {
                console.log("Going " + this.mph.toString() + " mph.");
        };

        exports.create = function() {
                var ret = Object.create(exports.prototype);
                ret.init();
                return ret;
        };

        return exports;
})();

然后我可以像这样构建派生类型:

var Car = (function () {
        var exports = {};
        exports.prototype = Object.create(Vehicle.prototype);
        exports.prototype.init = function() {
                Vehicle.prototype.init.apply(this, arguments);
                this.wheels = 4;
        };

        exports.create = function() {
                var ret = Object.create(exports.prototype);
                ret.init();
                return ret;
        };

        return exports; 

})();

使用此模式,每种类型都有自己的create()功能.