What is Hoisting in Javascript ??

In Javascript the variable declaration can be done at any place inside the function or inside the script. Where a variable is declared makes no difference because the javascript interpreter always move the variable declarations silently to the top of the scope where the variable is used.
For example, everyone will be fine the following javascript code.

<script>
  var num;
  num = 5;
  
  function foo(){
    alert(num);
  }
  foo();  
</script>

And, all will be able to guess that the function foo() will alert value 5.
However, the following code will confuse a lot of the developers, since the variable num is used before it is declared.

<script>
  num = 5;
  
  function foo(){
    alert(num);
  }
    
  foo();  
  var num;
</script>

The above code will run absolutely fine and will alert 5 just as in the previous example.
So what happened in example 2 ? What happened is Javascript Hoisting and it happened automatically behind the scenes.

  var num;
  num = 5;
  
  function foo(){
    alert(num);
  }
    
  foo();  

What above statement means is that

  
  function foo(){
    alert(num);
  } 
  foo();  

  var num = 5;

The above code will alert undefined, instead of 5, this is because only the declaration is hoisted and not initialization. The above code as read bu interpreter is as follows

  
  var num;

  function foo(){
    alert(num);
  }
  foo();  

  num = 5;

So it is very important to keep this in mind while writing your javascript code.

Points To Remember

• You can create objects of a function in javascript.
• Function can have both private and public methods.
• Functions can inherit other functions

Create an Object in Javascript

Let us create a User object in javascript.

var User = function() {
    _self = this;
    var _name;
    _self.getName = function() {
        return _name;
    }
    _self.setName = function(name) {
        _name = name;
    }
    _self.toString = function() {
        return "Person{name::" + _name + "}";
    }
}

Here User is a function

• name is a private variable and will not be accessible outside the User function.
• _self is used to save the this reference, this is done so that it does not mix with the this of the inner functions.
• getName, setName and toString are the public functions that can be called from an object of User function.

typeof User
"function"

Now let us create two Objects of the User function.

var user1 = new User();
var user2 = new User();

Both user1 and user2 are the objects of the User function, and they are not equal to each other, i.e they are two different objects.

typeof user1
"object"

typeof user2
"object"

user1 == user2
false

user1 === user2
false

Now let us call the functions on the user objects.

user1.getName()
undefined

user1.setName("ekiras");
undefined

user1.getName();
"ekiras"

user1.toString();
"Person{name::ekiras}"

Send JSON object as data in Ajax call.

Suppose you have  a JSON object associated with a variable say json  in our case, you can send this json value as data in the ajax call as follows.

var json = [{'id':1,'name':'user1'},{'id':2,'name':'user2'},{'id':3,'name':'user3'},{'id':4,'name':'user4'}]

function demo(url){
    $.ajax({
        method : 'POST',
        url : url,
        dataType: 'json',
        data : { objects :JSON.stringify(json)},
        success : function(data){
            console.log(data);
        },
        error : function(error){
            alert('OOps Something went wrong, please contact admin');
        }
    });
}

JSON.stringify() method will parse the json object and convert it to a string format that can be sent as data in the Ajax call.

you can also send other data with the json as follows

var json = [{'id':1,'name':'user1'},{'id':2,'name':'user2'},{'id':3,'name':'user3'},{'id':4,'name':'user4'}]

function demo(url){
    $.ajax({
        method : 'POST',
        url : url,
        dataType: 'json',
        data : { 'objects' :JSON.stringify(json), 'otherData' : 'value'},
        success : function(data){
            console.log(data);
        },
        error : function(error){
            alert('OOps Something went wrong, please contact admin');
        }
    });
}