If a non-letter argument is passed to the toLowerCase or toUpperCase method, the boolean value false is returned.

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Quizplus · Accepted Answer

The toLowerCase() and toUpperCase() methods in JavaScript are designed to work on strings. If a non-string argument is passed, these methods do not return a boolean value; instead, they attempt to convert the argument to a string and then apply the case transformation. If the conversion is not possible, it results in a TypeError.

If a Non-Letter Argument Is Passed to the ToLowerCase or ToUpperCase