JavaScript原型混乱

Question

I am new to JavaScript and experimenting with it these days. I came to know that JavaScript is prototype based. I tried executing below code:

var Person = function(name) {   
    this.name = name;
}
alert(Person.prototype);
var ram = new Person("Ram"); 
alert(ram.prototype); 

As expected, the first alert prints [object, Object] , I expect the second alert prints the same, but it doesn't, why?

Can any please explain it clearly?

Answer 1

Because the prototype property on functions isn't the function's prototype, it's a property that will get used to set the prototype of objects created via the new operator with that function.

You can access the object's prototype using ES5's Object.getPrototypeOf :

var Person = function(name) {   
    this.name = name;
};
alert(Person.prototype);
var ram = new Person("Ram"); 
alert(Object.getPrototypeOf(ram));

On Firefox and several other browsers, you can use an upcoming ES6 feature (for JavaScript in browsers): The __proto__ accessor property:

var Person = function(name) {   
    this.name = name;
};
alert(Person.prototype);
var ram = new Person("Ram"); 
alert(ram.__proto__);        // ES6 feature, but already fairly common

---

Note that __proto__ is a property inherited from Object.prototype , so if you create an object that doesn't inherit from Object.prototype (eg, var o = Object.create(null); or anything using that o as a prototype), you can only use Object.getPrototypeOf , not __proto__ .

Answer 2

The prototype property of your object Person is a property that you will only find in functions . To be clear, in JavaScript, functions are also objects with their own prototype . However, functions also have a special property named prototype which will become the prototype of every object made with that function as constructor.