function Person(name) { this.name = name; }; Person.prototype.getName = function() { return this.name; }; var p = new Person("ZhangSan"); console.log(p.constructor === Person); // true console.log(Person.prototype.constructor === Person); // true // 将上两行代码合并就得到如下结果 console.log(p.constructor.prototype.constructor === Person); // true function Person(name) { this.name = name; }; Person.prototype.getName = function() { return this.name; }; var p = new Person("ZhangSan"); console.log(p.constructor === Person); // true console.log(Person.prototype.constructor === Person); // true // 将上两行代码合并就得到如下结果 console.log(p.constructor.prototype.constructor === Person); // true 当时当我们重新定义函数的prototype时（注意：和上例的区别，这里不是修改而是覆盖），constructor属性的行为就有点奇怪了，如下示例： function Person(name) { this.name = name; }; Person.prototype = { getName: function() { return this.name; } }; var p = new Person("ZhangSan"); console.log(p.constructor === Person); // false console.log(Person.prototype.constructor === Person); // false console.log(p.constructor.prototype.constructor === Person); // false
为什么呢？
原来是因为覆盖Person.prototype时，等价于进行如下代码操作：
Person.prototype = new Object({ getName: function() { return this.name; } }); Person.prototype = new Object({ getName: function() { return this.name; } });
而constructor属性始终指向创建自身的构造函数，所以此时Person.prototype.constructor === Object，即是：
function Person(name) { this.name = name; }; Person.prototype = { getName: function() { return this.name; } }; var p = new Person("ZhangSan"); console.log(p.constructor === Object); // true console.log(Person.prototype.constructor === Object); // true console.log(p.constructor.prototype.constructor === Object); // true function Person(name) { this.name = name; }; Person.prototype = { getName: function() { return this.name; } }; var p = new Person("ZhangSan"); console.log(p.constructor === Object); // true console.log(Person.prototype.constructor === Object); // true console.log(p.constructor.prototype.constructor === Object); // true
怎么修正这种问题呢？方法也很简单，重新覆盖Person.prototype.constructor即可：
function Person(name) { this.name = name; }; Person.prototype = new Object({ getName: function() { return this.name; } }); Person.prototype.constructor = Person; var p = new Person("ZhangSan"); console.log(p.constructor === Person); // true console.log(Person.prototype.constructor === Person); // true console.log(p.constructor.prototype.constructor === Person); // true function Person(name) { this.name = name; }; Person.prototype = new Object({ getName: function() { return this.name; } }); Person.prototype.constructor = Person; var p = new Person("ZhangSan"); console.log(p.constructor === Person); // true console.log(Person.prototype.constructor === Person); // true console.log(p.constructor.prototype.constructor === Person); // true
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