Related Articles

Related Articles

Undefined Vs Null in JavaScript
  • Last Updated : 05 Nov, 2020

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

full-stack-img

My Personal Notes arrow_drop_up
Recommended Articles
Page :