It’s not always necessary, but it does have its uses. Suppose we wanted to make a copy method on the base Person
class. Like this:
// define the Person Class
function Person(name) {
this.name = name;
}
Person.prototype.copy = function() {
// return new Person(this.name); // just as bad
return new this.constructor(this.name);
};
// define the Student class
function Student(name) {
Person.call(this, name);
}
// inherit Person
Student.prototype = Object.create(Person.prototype);
Now what happens when we create a new Student
and copy it?
var student1 = new Student("trinth");
console.log(student1.copy() instanceof Student); // => false
The copy is not an instance of Student
. This is because (without explicit checks), we’d have no way to return a Student
copy from the “base” class. We can only return a Person
. However, if we had reset the constructor:
// correct the constructor pointer because it points to Person
Student.prototype.constructor = Student;
…then everything works as expected:
var student1 = new Student("trinth");
console.log(student1.copy() instanceof Student); // => true