NULL vs UNDEFINED vs EMPTY In Javascript

    By: Manu
    2 years ago

    Hi guys today we are going to see main difference in Null, Undefined and empty in javascript


    So when we create a variable in javascript without assigning any value for example here

    let name;
    

    This "name" variable will be "undefined".

    And to work with this variable either you assign default value or assign "null" as default value but it is totally optional.

    If you want to check the type of this "undefined" variable. It returns as "undefined".

    But in case of "null" typeof returns as "object".

    You can consider null as placeholder but with no value.


    Validation of Null and Undefined


    Be careful when validating here is why

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


    for validating we can do something like this

     // Here we will get alert message only if value is not null or not undefined
    
     if(name){
         alert(name);
     }
    


    What is Empty


    Enough about "null" and "undefined", Let's also consider empty. Empty can be anything Empty array or Empty object.

    So basically if you are expecting no data return but getting array with empty data kind of case. Here is how you validate a empty array.

    let names = ['Ron']; // Here we have array with single value
    
    // Here we check if array has values then alert message.
    
    if(names.length){
          alert('Array has value');
    }
    
    we can also do this
    
    
    // Here we check if array has at least one value then alert message.
    
    if(names.length > 0){
          alert('Array has value');
    }
    

    There might be case you see empty string as given here.

    let name = '';  // Here we are setting empty string as value
    
    // for validation we can check 
    
    if(name != ''){
        alert('Name is not empty string');
    }