ECMAScript 6（ES6） 特性概览和与ES5的比较11（上）-类

1.类的定义

面向对象风格和无反复套用，更加直观。

ECMAScript 6

class Shape {
    constructor (id, x, y) {
        this.id = id
        this.move(x, y)
    }
    move (x, y) {
        this.x = x
        this.y = y
    }
}

ECMAScript 5

var Shape = function (id, x, y) {
    this.id = id;
    this.move(x, y);
}
Shape.prototype.move = function (x, y) {
    this.x = x;
    this.y = y;
}

2.类的继承

面向对象风格和无反复套用，更加直观。

ECMAScript 6

class Rectangle extends Shape {
    constructor (id, x, y, width, height) {
        super(id, x, y)
        this.width = width
        this.height = height
    }
}
class Circle extends Shape {
    constructor (id, x, y, radius) {
        super(id, x, y)
        this.radius = radius
    }
}

ECMAScript 5

var Rectangle = function (id, x, y, width, height) {
    Shape.call(this, id, x, y);
    this.width = width;
    this.height = height;
};
Rectangle.prototype = Object.create(Shape.prototype);
Rectangle.prototype.constructor = Rectangle;
var Circle = function (id, x, y, radius) {
    Shape.call(this, id, x, y);
    this.radius = radius;
}

3.类的表达式继承

通过从产生函数对象的表达式扩展来支持mixin样式的继承。（注意：当然，泛型聚合函数通常由像这样的库提供）(不是很明白)

ECMAScript 6

var aggregation= (baseClass, ...mixins) => {
    let base = class _Combined extends baseClass {
        constructor (...args) {
            super(...args)
            mixins.forEach((mixin) => {
                mixin.prototype.initializer.call(this)
            })
        }
    }
    let copyProps = (target, source) => {
        Object.getOwnPropertypeNames(source)
            .concat(Object.getOwnPropertySymbols(source))
            .forEach((prop) => {
                if (prop.match(/^(?:constructor|prototype|arguments|caller|name|bind|call|apply|toString|length)$/))
                    return
                Object.defineProperty(target, prop, Object.getOwnPropertyDescriptor(source, prop))
            })
    }
    mixins.forEach((mixin) => {
        copyProps(base.prototype, mixin.prototype)
        copyProps(base, mixin)
    })
    return base
    
}

class Colored {
    initializer ()  { this._color = "white" }
    get color ()  {return this._color}
    set color (v) {this._color = v}
}

class ZCoord {
    initializer ()  {this._z = 0}
    get z ()        {return this._z}
    set z (v)       { this._z = v}
}

class Shape {
    constructor (x, y)  {this._x = x; this._y = y}
    get x()  {return this._x}
    set x(v)  {this._x = v}
    get y()  {return this._y}
    set y(v) {this._y = v}
}

class Rectangle extends aggregation(Shape, Colored, ZCoord) {}

var rect = new Rectangle(7, 42)
rect.z = 100
rect.color = "red"
console.log(rect.x, rect.y, rect.z, rect.color)

ECMAScript 5

var aggregation = function (baseClass, mixins) {
    var base = function () {
        baseClass.apply(this, arguments);
        mixins.forEach(function (mixin) {
            mixin.prototype.initializer.call(this);
        }.bind(this));
    };
    base.prototype = Object.create(baseClass.prototype);
    base.prototype.constructor = base;
    var copyProps = function (target, source) {
        Object.getOwnPropertyNames(source).forEach(function (prop) {
            if (prop.match(/^(?:constructor|prototype|arguments|caller|name|bind|call|apply|toString|length)$/))
                return
            Object.defineProperty(target, prop, Object.getOwnPropertyDescriptor(source, prop))
        })
    }
    mixins.forEach(function (mixin) {
        copyProps(base.prototype, mixin.prototype);
        copyProps(base, mixin);
    });
    return base;
};

var Colored = function () {};
Colored.prototype = {
    initializer: function ()  { this._color = "white"; },
    getColor:    function ()  { return this._color; },
    setColor:    function (v) { this._color = v; }
};

var ZCoord = function () {};
ZCoord.prototype = {
    initializer: function ()  { this._z = 0; },
    getZ:        function ()  { return this._z; },
    setZ:        function (v) { this._z = v; }
};

var Shape = function (x, y) {
    this._x = x; this._y = y;
};
Shape.prototype = {
    getX: function ()  { return this._x; },
    setX: function (v) { this._x = v; },
    getY: function ()  { return this._y; },
    setY: function (v) { this._y = v; }
}

var _Combined = aggregation(Shape, [ Colored, ZCoord ]);
var Rectangle = function (x, y) {
    _Combined.call(this, x, y);
};
Rectangle.prototype = Object.create(_Combined.prototype);
Rectangle.prototype.constructor = Rectangle;

var rect = new Rectangle(7, 42);
rect.setZ(1000);
rect.setColor("red");
console.log(rect.getX(), rect.getY(), rect.getZ(), rect.getColor());