Question

我想在javascript中使用父对象调用子方法我该怎么办？

var Shape = function () { }
    Shape.prototype.draw = function () {
        return "Generic shape called ";
    }

    var Circle = function () { }
    Circle.prototype = Object.create(Shape.prototype);
    Circle.prototype.draw = function () {
        return "I am from Circle";
    }

    var Rectangle = function () { }
    Rectangle.prototype = Object.create(Shape.prototype);
    Rectangle.prototype.draw = function () {
        return "I am from Rectangle";
    }

    var Triangle = function () { }
    Triangle.prototype = Object.create(Shape.prototype);

我想访问任何重写的方法，比如Rectangle，Circle，但是使用Shape对象，比如c＃我们可以做什么：Shape shape = new Circle（）shape.draw（）;它将调用子类的重写方法。我想在javascript中做同样的事情我该如何实现呢

Answer 1

如果在代码中使用Shape的任何子类（可以在运行时使用instanceof运算符进行检查），则可以简单地调用该方法。 Js运行时会自动从原型链中调用正确的方法。因此，如果代码中有一个名为myshape的对象，您可以：

if(myshape instanceof Shape){

    // invoke draw method
   myshape.draw();
}

Answer 2

var Shape = function () { }
    Shape.prototype.draw = function () {
        return "Generic shape called ";
    }
    Shape.prototype.val = 10;

    var Circle = function () { }
    Circle.prototype = Object.create(Shape.prototype);
    Circle.prototype.draw = function () {
        return "I am from Cirlce";
    }

    var Rectangle = function () { }
    Rectangle.prototype = Object.create(Shape.prototype);
    Rectangle.prototype.draw = function () {
        return "I am from Rectangle";
    }

    var Triangle = function () { }
    Triangle.prototype = Object.create(Shape.prototype);
    Triangle.prototype.draw = function () {
        return "I am from Triangle";
    }
        
    //Using Up casting (access value of parent object)
    var newCircle = new Circle();
    alert("newCircle: "+newCircle.draw()+" : "+newCircle.val);

如何在JavaScript中使用父对象调用子方法？

2 个答案: