Higher-Order Functions

A higher-order function takes a function as an argument, returns one, or both. You already use them: map, filter and forEach all take a function. Writing your own lets you capture a pattern once, such as "do this n times" or "only run this once", and reuse it with any behaviour plugged in.

How it reads

• repeat takes the action as a parameter and calls it
• once returns a new function that remembers whether it already ran
• ...args forwards whatever arguments the caller passes

Cloud tip: When two functions differ only in one small step, pass that step in as a function.