There are several differences between null and undefined, which are sometimes understood as the same.

1. Definition:

   • Null: It is the intentional absence of the value. It is one of the primitive values of JavaScript.

   • Undefined: It means the value does not exist in the compiler. It is the global object.

2. Type:

   
   
   
   

   Null: Object 

   Undefined: undefined

3. You can see refer to “==” vs “===” article.

    
    null == undefined // true
    null === undefined // false
   

   It means null is equal to undefined but not identical.

4. When we define a variable to undefined then we are trying to convey that the variable does not exist .
   When we define a variable to null then we are trying to convey that the variable is empty.

5. Differentiating using isNaN():
   You can refer to NaN article for better
   understanding.

   isNaN(2 +  null)      // false
   isNaN(2 + undefined) // true
   

6. Examples:

   • Null:

     null ? console.log("true") : console.log("false") // false
     

     Null is also referred as false.

   • Undefined:

     When variable is not assigned a value

     var temp;
     if(temp === undefined)
     console.log("true");
     else
     console.log("false");
     

     Output:

      true

     Accessing values which does not exist

     var temp=['a','b','c'];
     if(temp[3] === undefined)
     console.log("true");
     else
     console.log("false");
     

     Output:

     true