Modules &

Design Patterns

What is a Module?

Sections of code which can be moved, removed or added without disrupting the system as a whole (keeps code organized and separated)

The benefits of using modules

Maintainability - Lessens the dependency on other parts of the codebase
Namespacing - Unrelated code shares global variables
Reusability - Ability to reuse modules

How to use modules?

By using a the module pattern which is a design pattern.
A design pattern is used to describe a common approach to solving a programming task.
The module pattern is a popular way to write code that contains both public and private logic

IIFE

An IIFE runs as soon as it is defined
The function is executed once as the interpreter comes across them
Used for code that only needs to run one within a task
Commonly used as a wrapper around a set of code

Module patterns uses an IFFE (Immediately Invoked Function Expression) to return an object

Anonymous Closure


(function(){
  
  //salaries are private
  var salaries = [1000, 2000, 5000, 7000, 10000];
  
  var avgSalary = function(){
    var total = 0;
    for(var i = 0; i<salaries.length; i++){
      total += salaries[i];
      var avg = total/salaries.length;
    }
    return avg;
  }
  
 console.log(avgSalary()); //5000
  
}());

Hides variables (local) from the global scope
A closure is where an inner function has access to the outer
Enclosing function's variables

The Object Interface

var workerSalaries = (function(){
  var salaries = [10, 20, 30, 40, 50];
  
  return {
    median: 30,
    maxSalary: function(){
      var max = Math.max(salaries[0], salaries[4]);
      return max;
  }
  }
    
}()); //50

Self contained object
The variable is kept private inside the closure scope
returns an object that can be accessed

The Module Pattern

var openBank = (function(){
  //private
  var name = 'Jon Smith';
  var acctNo = 12345;
  var obj = {};
  
  
  //public var
  obj.balance = 300000;
  
  
  //public method
  obj.deposit = function(n){
    var newBal = this.balance + n;
    return newBal
  }
  
  return obj;
}())

console.log(openBank.balance)
console.log(openBank.deposit(1))
console.log(openBank.acctNo)

Create the object to be returned

The Revealing Module Pattern

var workerSalaries = (function(){
  var salaries = [10, 20, 30, 40, 50];
  
  var maxSalary = function(){
      var max = Math.max(salaries[0], salaries[4]);
      return max;
  }
  
  return {
    maxSalary: maxSalary
  }
    
}())

console.log(workerSalaries.maxSalary()) //50

Ensures that all variables and methods are kept private
Must be explicitly exposed to the public in the return object
Most popular of all the module patterns

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