Functional code...

doesntwork.js

function Penguin(name) {
    this.name = name;
    this.numLegs = 2;
}

// create your Emperor class here and make it inherit from Penguin
function Emperor(name){

   this.prototype = new Penguin(name);

}



var emperor = new Emperor("ralph");

// create an "emperor" object and print the number of legs it has

console.log(emperor.numLegs);

works.js

function Penguin(name) {
    this.name = name;
    this.numLegs = 2;
}

// create your Emperor class here and make it inherit from Penguin
function Emperor(name){

}

  Emperor.prototype = new Penguin(name);

var emperor = new Emperor("ralph");

// create an "emperor" object and print the number of legs it has

console.log(emperor.numLegs);

John, I'm curious as to why I can't define "this.prototype" in the class declaration. And I have to do it outside? Is it because I'm using prototype?

You're wanting to set the prototype of the Emperor "class". Inside the definition of the class (your "doesn't work" example), the Emperor class isn't yet defined, so you're most likely setting the prototype for some other object? The current context?

If you console.log(this) on line 9 of the "doesn't work" example, you'll find out what you're referencing.

Javascript "classes" aren't that great. Almost every JS framework creates their own inheritance structure. Good to know, but they're more of a hack then true inheritance that you get in other languages.