How to fix: "ReferenceError: undeclared identifier"

If you're seeing a ReferenceError: undeclared identifier message when trying to run a piece of JavaScript code, it means that the code is trying to use a variable or function that isn't defined. This can be caused by a spelling mistake, or by accidentally using a variable that's been declared in a different scope.

There are a few different ways to fix this error, depending on where it's occurring in the code.

Check the spelling of the variable or function name

This is the most common cause of "undeclared identifier" errors, and is usually easy to fix. Make sure you're using the correct spelling of the variable or function name, and that it's been declared in the correct scope.

Check the code for incorrect scoping

If you're sure that the variable or function name is spelled correctly, and that it's been declared in the correct scope, check the code for incorrect scoping. This can happen when you inadvertently use a variable or function that's been declared in a different scope.

For example, imagine you have a variable named myvar that's been declared in the global scope:

var myvar = "global variable";

If you then try to use myvar in a function, you'll get a ReferenceError: undeclared identifier error, because myvar isn't declared in the function scope.

To fix this, you need to make sure that you're using the correct scope for the variable or function you're trying to use. In the example above, you would need to declare myvar inside the function, like this:

function() {
	var myvar = "function variable";
}
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