javascript中的super

最新推荐文章于 2024-06-28 16:17:04 发布

原创最新推荐文章于 2024-06-28 16:17:04 发布 · 1.1k 阅读

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本文探讨了JavaScript中`super`关键字的使用，虽然其名称来源于德语中的`uber`，但`super`在JavaScript中作为保留字有着特殊含义。文章表达了作者对这种用法的个人感受。

/* Uber – access to the parent from a child object */
function Shape() { }
Shape.prototype.name = 'Shape';
Shape.prototype.toString = function() {
    var uber = this.constructor.uber;
    return uber ? uber.toString() + ', ' + this.name : this.name;
};

function Shape2D() { }
function A() { }
A.prototype = Shape.prototype;
Shape2D.prototype = new A();
Shape2D.prototype.constructor = Shape2D;
Shape2D.uber = Shape.prototype;
Shape2D.prototype.name = 'Shape 2D';

function Triangle(side, height) {
    this.side = side;
    this.height = height;
}
function B() { }
B.prototype = Shape2D.prototype;
Triangle.prototype = new B();
Triangle.prototype.constructor = Triangle;
Triangle.uber = Shape2D.prototype;
Triangle.prototype.name = 'Triangle';
Triangle.prototype.getArea = function() {
    return this.side * this.height / 2;
}

// test
var t = new Triangle(10, 10);
console.log(t.getArea());
console.log(t.toString());      // 输出 Triangle

var s = new Shape();
console.log(s.toString());      // 输出 Shape

var s2d = new Shape2D();
console.log(s2d.toString());    // 输出 Shape 2D

uber是德语的super的意思，因为super是javascript的保留字，所以使用德语的super。

用这种方式使用super，感觉还是好恶心

/* Isolating the inheritance part into a function */
function extend(Child, Parent) {
    var F = function() { };
    F.prototype = Parent.prototype;
    Child.prototype = new F();
    Child.prototype.constructor = Child;
    Child.uber = Parent.prototype;
}

function Shape() { }
Shape.prototype.name = 'Shape';
Shape.prototype.toString = function() {
    var uber = this.constructor.uber;
    return uber ? uber.toString() + ', ' + this.name : this.name;
}

function Shape2D() { }
extend(Shape2D, Shape);
Shape2D.prototype.name = 'Shape 2D';

function Triangle(side, height) {
    this.side = side;
    this.height = height;
}
extend(Triangle, Shape2D);
Triangle.prototype.name = 'Triangle';
Triangle.prototype.getArea = function() {
    return this.side * this.height / 2;
}

// test
var t = new Triangle(10, 10);
console.log(t.toString());

把继承部分封装到extend函数中，看起来清晰了很多