是否有必要在JavaScript中具有原型继承，以便我们可以动态传播添加的新属性？

Question

I have been brushing up on prototypal inheritance in JavaScript and I have a major question about its necessity. I am unable to grasp the reasons why it is very important. I have been running the basic code snippet shown below :

 function Employee() { this.name = "geetha"; this.dept = "general"; } Employee.prototype.designation = "nothing"; function Manager() { Employee.call(this); this.title = "mr"; } Manager.prototype = Object.create(Employee.prototype); var mark = new Manager; console.log(mark.name); console.log(mark.dept); console.log(mark.title); console.log(mark.designation); 

 <script src="https://getfirebug.com/firebug-lite-debug.js"></script> 

In the above snippet, if I remove

 Manager.prototype = Object.create(Employee.prototype); 

I can see it only impedes me from adding a new property on the go for the "Employee" constructor such that it trickles down to the objects it is a prototype of. Otherwise, if I am content with the properties already defined, I don't really need to make "Employee" the prototype of "Manager". The constructor call of Employee from inside Manager would accomplish the getting of its properties. So am I missing something really important in this concept?

Thanks!

Answer 1

If you don't use the line

Manager.prototype = Object.create(Employee.prototype);

then you are not actually using inheritance. You are simply using the Employee constructor to initialise the variables in the Manager instance just as they would be initalised in an Employee instance.

The thing to note is this line

Employee.prototype.designation = "nothing";

If you do not use inheritance then the property designation will not available to Manager instances because it will not be in the prototype chain.