The document discusses inheritance in JavaScript. It shows how objects like cow and chicken can inherit properties and methods from a parent animal object to avoid duplicating code, using Object.setPrototypeOf(). It demonstrates that while JavaScript doesn't have classes, inheritance can be achieved through prototypes. Objects can check an object's prototype to see if it inherits certain properties or methods from its parent.

1. JAVASCRIPT
INHERITENCE

2. WHY DO YOU NEED INHERITENCE?
var cow = {
eat: function() { console.log("yum") },
poo: function() { console.log("poop") },
moo: function() { console.log("moo") }
}
var chicken = {
eat: function() { console.log("yum") },
poo: function() { console.log("poop") },
cluck: function() { console.log("cluck") }
}

3. DON'T REPEAT YOURSELF
var animal = {
eat: function() { console.log("yum") },
poo: function() { console.log("poop") }
}
var cow = {
moo: function() { console.log("moo") }
}
Object.setPrototypeOf(cow,animal);
var chicken = {
cluck: function() { console.log("cluck") }
}
Object.setPrototypeOf(chicken,animal);
cow.poo(); // poop

4. JAVASCRIPT ISN'T CLASSY

5. I AM A COW.
cow.poop(); // ???

6. Does a cow know how to poo?
cow.hasOwnProperty('poo') // false
SHUCKS.

7. BUT A COW IS ALSO AN ANIMAL, RIGHT?
Object.getPrototypeOf(cow) // Object {eat: function, poo: function}
YUP.

8. ..AND AN ANIMAL CAN POO, RIGHT?
animal.hasOwnProperty('poo') // true
YAY!

9. POOP

10. JAVASCRIPT ISN'T CONSTRUCTIVE.

11. var Animal = function(name) {
this.name = name;
}
Animal.prototype = {
eat: function() { console.log("yum") },
poo: function() { console.log("poop") }
}
var beast = new Animal('Keith');
console.log( beast.name ); // Keith
beast.eat(); // yum