Javascript inheritance different extend functions implementation

Question

In the book Pro Javascript design patterns one of the ways for implementing inheritance is by using an extend function.

function extend(subClass, superClass) {
   var F = function() {};
   F.prototype = superClass.prototype;
   subClass.prototype = new F();
   subClass.prototype.constructor = subClass;
}

Sample usage

function Person(name) {
    this.name = name;
}
Person.prototype.getName = function() {
    return this.name;
}
function Author(name, books) {
    Person.call(this, name);
    this.books = books;
}
extend(Author, Person);

So, why can't the same function be implemented this way?

function extend(subClass, superClass) {
    subClass.prototype.__proto__ = superClass.prototype
}

What is the difference between the two implementations if they are not the same?

__proto__ was not supported by IE < 11 developer.mozilla.org/en/docs/Web/JavaScript/Reference/… among other things — Xotic750
– Xotic750, Commented Jun 24, 2017 at 18:12

JLRishe · Accepted Answer · 2017-06-24 18:40:18Z

1

__proto__ is not a standard JavaScript feature and it is not guaranteed to work. Most modern browsers will allow you to use it, but it's technically supposed to be an internal mechanism and you should not use it.

So that's most likely why the example didn't do it that way.

answered Jun 24, 2017 at 18:40

JLRishe

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