Question

Greetings,

After reading the following article I have a question:
https://developer.mozilla.org/en/Introduction_to_Object-Oriented_JavaScript

In the inheritance example, the Person constructor doesn’t take any parameters. How would this same example look if I were to add one and call it from the Student constructor?

Thanks!

Answer 1

Well, a way that you can re-use the logic of the Person constructor is invoking it with call or apply, for example:

function Person(gender) {
  this.gender = gender;
}

function Student(gender) {
  Person.apply(this, arguments);
}
Student.prototype = new Person(); // make Student inherit from a Person object
Student.prototype.constructor = Student; // fix constructor property

var foo = new Student('male');
foo.gender;             // "male"
foo instanceof Student; // true
foo instanceof Person;  // true

If you want to prevent the execution of the Person constructor when is called without arguments (like in the line: Student.prototype = new Person();), you can detect it, e.g.:

function Person(gender) {
  if (arguments.length == 0) return; // don't do anything
  this.gender = gender;
}