In TypeScript, why isn't a boolean value or typeguard considered as a typeguard within a function?

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A boolean value is not considered a typeguard in TypeScript because it is simply a truthy or falsy value that cannot provide any additional information about the type of a variable. A typeguard, on the other hand, is a way to narrow down the type of a variable based on a specific condition that is checked at runtime. For example, using an "instanceof" check or typeof check.

Similarly, a typeguard function must return a boolean value that tells TypeScript whether a variable is of a certain type or not. If a typeguard function returns anything other than a boolean value, it will not be considered a valid typeguard in TypeScript.