javascript check if undefined

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.

Check if JavaScript variable is NULL or Undefined
Check if JavaScript variable is NULL or Undefined

In JavaScript mostly we getting an error statement called an undefined variable. Before we start, first we learn about the difference between 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:


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


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


JavaScript typeof

Above we use JavaScript typeof in many places. So I want to clear you what is use of the JavaScript typeof operator. Also used for checking JavaScript array is empty or not.

The typeof operator returns a string indicating the type of variable

A Complete Lesson about how to Check if a 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.

Here is the JavaScript Exception solver, you can try it.   

Also Check:

Know more about JavaScript:  

Happy Coding…

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By Bikash

My name is Bikash Kr. Panda. I own and operate PHPCODER.TECH. I am a web Programmer by profession and working on more than 50 projects to date. Currently I am working on the web-based project and all the CMS and frameworks which are based on PHP.

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