Today, we are going to talk about how to check if a variable is declared in JavaScript. In JavaScript, there is a built-in function to check whether a variable is defined or undefined name typeof.

What are declared variables in JavaScript? #

Let's talk about what "declared variables" are. A declared variable means that it has been given an identifier and assigned some value (or none).

How to check if a variable is declared or not. #

By using the typeof() operator, we can easily check if a particular variable has been declared or not. If the item hasn't been set, the typeof() operator will return "undefined". Otherwise, it returns its actual data type (string, boolean etc.).

<script>
 const myVar; //Declaration variable without assigning value.
 console.log(typeof myVar); // output "undefined".
</script>

Now let's look at another example of setting some values.

<script>
 const myVar = "Hello"; //Declaration variable with assigning value.
 console.log(typeof myVar); // output "string".
</script>