Type narrowing and guarding

Type narrowing is the process of working out from a supertype like any or unknown whic type the value should be in the x course of your code. This is necessary since a process will not necessarily always return or involve homogenous types.

Related to this is type guarding: ensuring that a value is of the suitable type as a factor of control flow. For instance using typeof to ensure that an input is numerical before proceeding with a function’s logic.