Understanding module design pattern in javascript

Question

I am not very good in JavaScript. so when I saw a block of code now then many area is not clear. So someone please help me to understand.

I know this below way peopl

Answer 1

var HMS = HMS || {}; 

that expression defines the var HMS to HMS or empty object if it is not defined is a short hand for

if(HMS) {
  var HMS = HMS;
} else {
  var HMS = {};
}

2) You are creating an object from an IIFE

They are declaring and empty object if it does not exist, and decorating it with the methods/functions once the function below its executed. is the same as this:

var HMS = {
   PatientModel : function () {},
   PatientViewModel : function () {}, 
}

3) And that is why they use HMS inside the function.

var HMS = {};
HMS.PatientModel = function() {};
HMS.PatientViewModel = function() {};

You should read about Closures, IIFE, and How to “properly” create a custom object in JavaScript?

Sample and short explanation of closure:

A closure is when you have access to variables that are not in the lexical scope of the function For example, a function declared inside another function, will have access to the parent variables.

eg:

(function(){
    var a = 1;

    function mainFunction() {

        function innerFunction() {
            var b = 2

            function subFunction() {
                console.log(a); //We have access to "a" here.
                console.log(b); //We have access to "b" here.
            }

           subFunction();
        }


        innerFunction();
        console.log(a); //We have access to "a" here.
        console.log(b); //We dont have access to "b" here. //error
    }
    mainFunction();

})();
console.log(a);  //We dont have access to "a" here. //error