Is there a good use case for the constructor property in Javascript?

Question

First off, this question is not \"what does the constructor property do?\" - There\'s plenty of good documentation on exactly what it is and how it works: It\'s a r

Answer 1

One of the good use cases is implementation of "inheritance" and "classes in javascript. Let's consider the following example:

// define the Person Class
function Person() {}

Person.prototype.walk = function(){
  alert ('I am walking!');
};
Person.prototype.sayHello = function(){
  alert ('hello');
};

// define the Student class
function Student() {
  // Call the parent constructor
  Person.call(this);
}

// inherit Person
Student.prototype = new Person();

// correct the constructor pointer because it points to Person
Student.prototype.constructor = Student;

// replace the sayHello method
Student.prototype.sayHello = function(){
  alert('hi, I am a student');
}

// add sayGoodBye method
Student.prototype.sayGoodBye = function(){
  alert('goodBye');
}

var student1 = new Student();
student1.sayHello();
student1.walk();
student1.sayGoodBye();

// check inheritance
alert(student1 instanceof Person); // true 
alert(student1 instanceof Student); // true

As you can see we've inherited Person, by reassigning Student.prototype to new Person();, but then we need to reassign constructor back to Student as we want to create instance of Student class, but not a Person.

UPDATE

Btw, more real-world example of inheritance in javascript is to use intermediate function, so Person object will not be created during definition stage:

// inherit Person
function F() {}
F.prototype = Person.prototype;
Student.prototype = new F();