CODEWITHSUNDEEP
javascriptinheritanceconstructorprototypal-inheritance
Misha Moroshko
Misha Moroshko

Reputation: 171321

Is "Subclass.prototype.constructor = Subclass" needed when inheriting objects in Javascript?

Consider the following example where Student inherits from Person:

function Person(name) {
    this.name = name;
}
Person.prototype.say = function() {
    console.log("I'm " + this.name);
};

function Student(name, id) {
    Person.call(this, name);
    this.id = id;
}
Student.prototype = new Person();
// Student.prototype.constructor = Student;    // Is this line really needed?
Student.prototype.say = function() {
    console.log(this.name + "'s id is " + this.id);
};

console.log(Student.prototype.constructor);   // => Person(name)

var s = new Student("Misha", 32);
s.say();                                      // => Misha's id is 32

As you can see, instantiating a Student object and calling its methods works just fine, but Student.prototype.constructor returns Person(name), which seems wrong to me.

If I add:

Student.prototype.constructor = Student;

then Student.prototype.constructor returns Student(name, id), as expected.

Should I always add Student.prototype.constructor = Student?

Could you give an example when it is required ?

Upvotes: 3

Views: 1508

Answers (1)

nahab
nahab

Reputation: 1354

Read this SO question Prototype inheritance. obj->C->B->A, but obj.constructor is A. Why?.

It should give your an answer.

Upvotes: 1

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