假设标准继承模式：

// class A:

function ClassA(foo) {
    this.foo = foo;
}

ClassA.prototype.toString = function() {
    return "My foo is " + this.foo;
};

// class B:

function ClassB(foo,bar) {
    ClassA.call(this,foo);
    this.bar = bar;
}

ClassB.prototype = new ClassA();

ClassB.prototype.toString = function() {
    return "My foo/bar is " + this.foo + "/" + this.bar;
};

我无法弄清楚构造函数中要调用的内容：

function Image2() {
    // this doesn't work:
    Image2.prototype.constructor.call(this);
    // neither does this (only applies to <img>,no equivalent for <span> etc.):
    Image.call(this);
}

Image2.prototype = new Image(); // or document.createElement("img");

Image2.prototype.toString = function() {
    return "My src is " + this.src;
};

这是不可能的吗？还是有某种方法？谢谢. =)