When dealing with heterogeneous arrays in TypeScript, I frequently want to use list.filter(...) to extract an array of all one type. However without extra effort, TypeScript will implicitly type the result of that filtering the same as the input. For example: Notice how numbers and strings are still considered…

You can read more about user defined type guards at the official documentation, but in summary they are basically awesome. If you find an urge to write someArg as someType outside of a type guard function, ask yourself if a type guard could be cleaner. Consider the following: Line…