What is different between snapshot and prevState, prevProps from componentDidUpdate in react?

Question

I just started to studying React.

When learning LifeCycle and I wonder about componentDidUpdate method.

As I read componentDidUpdate method can have three params (prevProps, prevState, snapshot). If I can find out prevState from componentDidUpdate what is the snapshot for?

It may not important but I just got curious

Answer 1

From the componentDidUpdate docs:

If your component implements the getSnapshotBeforeUpdate() lifecycle (which is rare), the value it returns will be passed as a third “snapshot” parameter to componentDidUpdate(). Otherwise this parameter will be undefined.

getSnapshotBeforeUpdate

getSnapshotBeforeUpdate() is invoked right before the most recently rendered output is committed to e.g. the DOM. It enables your component to capture some information from the DOM (e.g. scroll position) before it is potentially changed. Any value returned by this lifecycle will be passed as a parameter to componentDidUpdate().

This use case is not common, but it may occur in UIs like a chat thread that need to handle scroll position in a special way.

A snapshot value (or null) should be returned.

Use-cases appear mostly related to querying the DOM, or anything that can't be derived from state or props.