JavaScript Check the existence of variable

In this article, we will explore different methods to check the existence of a variable in JavaScript.

We'll cover some approaches that help us determine if a variable is defined or not.

Using the typeof Operator #

The typeof operator allows us to check the data type of a variable or expression. We can use this operator to determine if a variable exists by checking if its type is not equal to undefined.

1. The typeof operator returns a string representing the data type of the variable.
2. It doesn't work correctly for variables declared with the let or const keywords if they are not defined in the current scope.
3. It will return false for variables that are explicitly set to undefined.

Check variable exists or not using try and catch #

We can use a try and catch block to check if a variable exists. By attempting to access the variable within the try block, we can catch any ReferenceError that may occur if the variable is not defined.

1. If myVariable is declared but not defined, it will not throw an error, and the catch block won't execute.
2. This method is suitable for variables declared with let or const in any scope, not just the global scope.
3. It will work correctly for variables explicitly set to undefined.