Check if JavaScript variable is NULL or Undefined

By | June 3, 2020

Check if JavaScript variable is NULL or Undefined, here we are learning about some very basic JavaScript functionality. At the time of Website development, we use NULL which is an assignment value. In JavaScript mostly we getting an error statement called “undefined variable”. Before we start with “Check if JavaScript variable is NULL or Undefined”, first we learn about the difference between NULL or Undefined.

Check if JavaScript variable is NULL or Undefined

Difference between JavaScript NULL or JavaScript Undefined

In JavaScript, you can check the variable is Undefined or Null or empty string or has a value. Below are some points for clarifying the difference.
  1. In JavaScript Undefined means, the variable has declared but no value has assigned to it. Check below example:

    Output: Undefined
    Undefined

  2. JavaScript Null is an assignment value, which means a variable has no value. And null value has object type. See below example:

    Output: Null
    Object

 
 
 
 
Before move forward, I have to clear that JavaScript NULL and JavaScript Undefined both are two distinct types.
 
  • Undefined is typing itself
  • A null is an Object

and,

Javascript typeof

Above we use “JavaScript typeof” in many places. So I want to clear you what is use of the JavaScript typeof operator.
 
The typeof operator returns a string indicating the type of variable“.
 
 
Example:

A complete lesson about Check if JavaScript variable is NULL or Undefined

 
Let’s talk about JavaScript check undefined or JavaScript empty array using some examples, here we start,
Using the above code you get the value “true” if the value is not,
  • Null
  • Undefined,
  • empty string
  • NaN
  • 0
  • False
You van also check like this,
 
 
Here are all the explanations above about Check if the Javascript variable is NULL or Undefined. If you have any question please comment below.
 
 
Know more about JavaScript: https://en.wikipedia.org/wiki/JavaScript
 
Happy Coding…

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