JS中的constructor
// constructor属性始终指向创建当前对象的构造函数。比如下面例子:比如下面例子: //var foo = new Array(1, 56, 34, 12); var arr = [1, 56, 34, 12]; console.log(arr.constructor === Array); // true //var foo = new Function(); var Foo = function() {}; console.log(Foo.constructor === Function); // true //由构造函数实例化一个obj对象 var Foox = new Foo(); console.log(Foox.constructor === Foo); // true //将上面两段代码合起来,就得到下面的结论 console.log(Foox.constructor.constructor === Function); // true //但是当constructor遇到prototype时,有趣的事情就发生了。 我们知道每个函数都有一个默认的属性prototype,而这个prototype的constructor默认指向这个函数。如下例所示: 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; } }); //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 //此处的Object即为下面的Object //Person.prototype = new Object({ // getName: function() { // return this.name; // } //}); //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) { console.log(this); //Person(ZhangSan) 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 // 顺带说说继承,以上的称为原型继承,下面的继承只能继承私有属性 // function Father(name){..this..} // Father()之中的this在编译阶段不会赋值,最后会指向new Father()对象 function Father(name){ this.name = "LiuYashion"; this.age = 23; }; Father.prototype.getName = function(){ console.log(this) // 这里的this指向的是new Father(),即temp2 console.log(this.name); }; function Son(){ //Father.call(this,["name","age"]); Father.apply(this,["name","age"]); //call跟apply的区别只在于后面参数的传法,不赘述 }; var temp1 = new Son(); console.log(temp1.name+" "+temp1.age); //LiuYashion 23 var temp2 = new Father(); temp2.getName(); //LiuYashion