JavaScript ReferenceError – variable is not defined

This JavaScript exception variable is not defined and occurs if there is a non-existent variable that is referenced somewhere.

Message:

ReferenceError: "x" is not defined

Error Type:

ReferenceError

Cause of Error:

There is a non-existent variable that is referenced somewhere in the script. That variable has to be declared or make sure the variable is available in the current script or scope.

Example 1: In this example, the variable(val1) is being accessed from the outside of the function, So the error has not occurred.

Output:

ReferenceError: 'val1' is not defined

Example 2: In this example, the variable(GFG) is not defined, So the error has occurred.

Output:

ReferenceError: 'GFG' is not defined