Develop Reference

Why isn't this anonymous function returning?

I know this is complete purposeless code I'm just experimenting with anonymous functions with code I have already written and had at hand. I can't figure out though why it array isn't returning?
(function() {
function Employee(name, age, pay) {
this.name = name;
this.age = age;
this.pay = pay || 800;
}
function Manager(name, age, pay) {
Employee.call(this, name, age, pay);
this.reports = [];
}
Manager.prototype = Object.create(Employee.prototype);
Manager.prototype.addReport = function(report) {
this.reports.push(report);
}
function Cashier(name, age, pay) {
Employee.call(this, name, age, pay);
}
Cashier.prototype = Object.create(Employee.prototype);
var ary = [Cashier, Manager];
return ary;
}());

...why it array isn't returning?
It is. You're just not doing anything with that return value; see *** comment on first line:
var result = (function() { // ****
function Employee(name, age, pay) {
this.name = name;
this.age = age;
this.pay = pay || 800;
}
function Manager(name, age, pay) {
Employee.call(this, name, age, pay);
this.reports = [];
}
Manager.prototype = Object.create(Employee.prototype);
Manager.prototype.addReport = function(report) {
this.reports.push(report);
}
function Cashier(name, age, pay) {
Employee.call(this, name, age, pay);
}
Cashier.prototype = Object.create(Employee.prototype);
var ary = [Cashier, Manager];
return ary;
}());
console.log(result);

Actually, this code is returning two constructor function objects. Try running it on your console :-

Creating a Class Method

function Person(firstName = "John", lastName = 'Doe', age = 0, gender = 'Male') {
this.firstName = firstName;
this.lastName = lastName;
this.age = age;
this.gender = gender;
this.sayFullName = function() {
return this.firstName + " " + this.lastName
};
}
Person.prototype.greetExtraTerrestrials = function(raceName) {
return `Welcome to Planet Earth ${raceName}`;
};
What is wrong with this code? Doesn't it create a class method called greetExtraTerrestrials?

Don't place that function on prototype, place that on Class itself like
Person.greetExtraTerrestrials = function(raceName) {
return `Welcome to Planet Earth ${raceName}`;
};
and call it like
Person.greetExtraTerrestrials('ABC');

You can do both! The difference in
class Person(...) {
...
}
Person.myFunction = function(val) { // This is a public function
return val;
}
Person.prototype.myFunction = function(val) { // This is a private function
return val;
}
is how you access it.
Access the public function :
var r = Person.myFunction("Hello!");
console.log(r);
Access the private function:
var person1 = new Person(...);
var r = person1.myFunction("Hello!");
console.log(r);
See also this question.

Actually it works, but firstly you need to create an instance of Person to be able call its methods. For example:
var john = new Person("John");
console.log(john.greetExtraTerrestrials("predator"));

JavaScript OOP: Uncaught TypeError: is not a function

Have trouble with object creation. Console says that something wrong in the last line. Please tell how it should be, I more familar with Java, so this is little bit confusing for me.
var dog = {
name:"Dog",
age:"11",
getName : function() {
alert(this.name);
}
}
function Dog(name, age) {
this.name = name;
this.age = age;
}
var d1 = new Dog("Rex", 8);
d1.getName();

Your dog is just a simple Object literal,
that means that your getName is bound to it, not to your Dog class.
You can make that function a method of Dog instead:
/*var dog = {
name:"Dog",
age:"11",
getName : function() {
alert(this.name);
}
}*/
function Dog(name, age) {
this.name = name;
this.age = age;
}
Dog.prototype.getName = function() {
console.log( this.name );
}
var d1 = new Dog("Rex", 8);
d1.getName(); // "Rex"
Here's a variant that uses your settings "defaults"
function Dog() {
this.name = "Dog"; // Default name
this.age = 11; // Default age
}
Dog.prototype.getName = function() {
console.log( this.name );
}
var d1 = new Dog();
d1.name = "Rex"; // Override default name
d1.getName(); // "Rex"

You can use class with syntaxic sugar to properly create objects in ES6.
In your exemple that would write like this :
'use strict';
class Dog{
constructor(name, age){
this.name = name;
this.age = age;
}
getName(){
console.log(this.name);
}
}
let doggy = new Dog("krypto", 125);
doggy.getName();

Traditional OO in JavaScript
function Dog(name, age) {
this.name = name || "Dog";// if the name is not given, it defaults to "Dog"
this.age = age || "11";
}
Dog.prototype.getName = function() {
alert(this.name);
}
var d1 = new Dog("Rex", 8);
d1.getName();
More Explicit OO in JavaScript
function createDog(name, age) {
// create a new dog and return it
var dog = {
name: name || "Dog",// if the name is not given, it defaults to "Dog"
age: age || "11"
};
return dog;
}
createDog.getName = function(dog) {
// explicit dog as 1st parameter
alert(dog.name);
}
//createDog is a normal function that returns something, no "new" needed
var d1 = createDog("Rex", 8);
createDog.getName(d1);

How do you put an if/else statement inside an object key?

I'm trying to create a Person class. The person's age would be a random number, determined by an if/else statement. Right now it seems to only work if I place the function outside of the object, or as a separate key.
function age(x) {
if (x.toLowerCase().charCodeAt(0) <= "g".charCodeAt(0)) {
return Math.floor(Math.random()*40+1);
}
else {
return Math.floor(Math.random()*40+41);
}
}
function person(name) {
this.name = name;
this.age = age(name);
}
var people = {
joe: new person("Joe")
};
console.log(people.joe.age);
\\ returns a number 41-80
Is there a way for me to put the function directly into the "this.age" key and have the same thing happen, like so:
function person(name) {
this.name = name;
this.age = function age() {
if (this.name.toLowerCase().charCodeAt(0) <= "g".charCodeAt(0)) {
return Math.floor(Math.random()*40+1);
}
else {
return Math.floor(Math.random()*40+41);
}
};

You can execute the function immediately:
function person(name) {
this.name = name;
this.age = (function age() {
if (this.name.toLowerCase().charCodeAt(0) <= "g".charCodeAt(0)) {
return Math.floor(Math.random()*40+1);
}
else {
return Math.floor(Math.random()*40+41);
}
})();
};

function person(name) {
this.name = name;
this.age = (function age() {
var x = this.name.toLowerCase().charCodeAt(0) <= "g".charCodeAt(0))?1:41;
return Math.floor(Math.random()*40+x);
})();
};
doing (function(){})() you're executing it.
(function(){}) //this converts the function into a statement
() // this executes

You have to define the closure (function) and execute it right on.
function person(name) {
this.name = name;
this.age = (function age() {
var x = this.name.toLowerCase().charCodeAt(0) <= "g".charCodeAt(0)) ? 1 : 41;
return Math.floor(Math.random()*40+x);
})();
};

How to do prototypal inheritance in JavaScript?

I've tried several ways but I couldn't do it.
On the next example I want the Soldier gets all properties of Person, and allowing to add more properties. How to do it correctly?
function Person(name, age) {
this.name = name;
this.age = age;
}
Person.prototype.hi = function (message) {
console.log(message + "!!!");
};
var Soldier = new(Person); // it is not the way to do it
Soldier.prototype.good_hi = function (message) {
console.log("Sir! " + message + ", sir!");
};

You don't have a Soldier constructor. You need to make that first. Then you'd apply the Person constructor to new Soldier instances.
function Person(name, age) {
this.name = name;
this.age = age;
}
Person.prototype.hi = function (message) {
console.log(message + "!!!");
};
function Soldier(name, age) {
Person.apply(this, arguments);
}
Soldier.prototype = Object.create(Person.prototype); // is better
Soldier.prototype.constructor = Soldier;
Soldier.prototype.good_hi = function (message) {
console.log("Sir! " + message + ", sir!");
};
Then use it like this:
var s = new Soldier("Bob", 23);
s.good_hi("Hello");
DEMO: http://jsfiddle.net/3kGGA/