以下两个声明之间的区别是什么以及何时应该使用它们

Question

I am learning javascript. I am confused between the following two notations where the newly created objects inherit the properties. How are they different and when should i use them?

Code 1:

 var Vehicle = function Vehicle() {
       this.wheel=2
    }

    var vehicle = new Vehicle();
    alert(vehicle.wheel);

Code 2:

 var Vehicle = function Vehicle() {
    }
    Vehicle.prototype.wheel = 4;
    var vehicle = new Vehicle();
    alert(vehicle.wheel);

When is the keyword prototype used?

Answer 1

Properties defined on prototype will be shared by all the instances. So if you create 10 vehicles, they just share the wheel property(only one), and each vehicle doesn't have a wheel property on itself .

Answer 2

最重要的区别是，当您向函数原型添加属性并从中实例化新对象时，通过加强继承链而不是直接在对象上来访问新对象中的属性。

Answer 3

You need to read about prototype, there were lots of threads in stackoverflow, do a little search. For example read this article . Or grab a book which is the best approach to learn something, I recommend this great book, JavaScript: The Good Parts

In general it's much better using prototype in terms of memory consumption and prototype chain that can be extendable.