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January 30, 2023 ›
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How to check if a variable is declared in JavaScript
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>
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