How can I split my javascript code into separate files?

Question

I'm reading the Javascript Guide from Mozilla And when they contrasted JS to Java , It got me thinking, Java code is easily split up with each class in his own file. after futher search , I understand that the same can be accomplished in JS with namespacing and module pattern - I messed around with it but got very confused ( especially with calling a constructor declared in File1.js into File2.js )

so here is the hierarchy:

But i just can't figure out how to properly make it works

how do i simply go from

//employe.js
function Employee () {
  this.name = "";
  this.dept = "general";
}

function Manager () {
  this.reports = [];
}
Manager.prototype = new Employee;

function WorkerBee () {
  this.projects = [];
}
WorkerBee.prototype = new Employee;

function SalesPerson () {
  this.dept = "sales";
  this.quota = 100;
}
SalesPerson.prototype = new WorkerBee;

to this :

 // employe.js
function Employee () {
  this.name = "";
  this.dept = "general";
}

 // Manager.js   
function Manager () {
  this.reports = [];
}
Manager.prototype = new Employee;

 // WorkerBee.js     
function WorkerBee () {
  this.projects = [];
}
WorkerBee.prototype = new Employee;

 // SalesPerson.js      
function SalesPerson () {
 this.dept = "sales";
 this.quota = 100; 
 }
SalesPerson.prototype = new WorkerBee;

Answer 1

You should have one global namespacing object which every module has to access and write to. Modify your files like so:

// employe.js

window.myNameSpace = window.myNameSpace || { };

myNameSpace.Employee = function() {
    this.name = "";
    this.dept = "general";
};

and Manager.js could look like

// Manager.js

window.myNameSpace = window.myNameSpace || { };

myNameSpace.Manager = function() {
    this.reports = [];
}
myNameSpace.Manager.prototype = new myNameSpace.Employee;

This is of course a very simplified example. Because the order of loading files and dependencies is not child-play. There are some good librarys and patterns available, I recommend you looking at requireJS and AMD or CommonJS module patterns. http://requirejs.org/

Answer 2

You don't need to do anything differently. Just include the script files and they work as if it was a single file.

Javascript doesn't have file scope. Once the code is parsed it doesn't matter where the code came from.

Answer 3

For small and medium projects like a website or game, the native namespacing and constructors work very well. They are a poor choice when the loading order is too complex to handle without some sort of autoloading.

index.html:

<script src="Employee.js"></script>
<script src="Manager.js"></script>

Manager.js:

var Manager = function() {
    var employee1 = new window.Employee(this);
    var employee2 = new window.Employee(this);
};

Employee.js:

var Employee = function(boss) {
    // work stuff here
    this.wage = 5;
};

Note, properties inside the employee constructor function are visible to the manager. The new word signals a constructor. This is also possible without a constructor by returning an object with properties instead of a function as shown above.