I'm going to assume you're familiar with Redux. If not, there's a brief section on it here. useReducer allows us to do Redux-style reducers but inside a hook. Here, instead of having a bunch of functions to update our various properties, we have one reducer that handles all the updates based on an action type. This is a preferable approach if you have complex state updates or if you have a situation like this: all of the state updates are very similar so it makes sense to contain all of them in one function.
Complete Intro to React v7
