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JavaScript React Basics (2018) Understanding State Update State Based on Previous State

Why use prevState?

I don't understand why we use prevState because basically, prevState shld be something like

let preState = this.setState

before using it, (I m using my own imagination because we never assigned prevState to any value so what is prevState?

prevState is the state value BEFORE that callback is applied. It isn't set here because prevState is set by React, as we extend React.Component with our class based component we can access the methods set by React such as prevState.

travis halarewich
travis halarewich
9,165 Points

I do not believe prevState is set by React like Dan Sutherland has mentioned. I’m pretty sure it is just a random name made up like all parameters for functions are. Hopefully someone who knows 100% can chime in

1 Answer

Waylan Sands
PLUS
Waylan Sands
Courses Plus Student 5,824 Points

prevState was just a random name he gave for the argument added to the setState function. When you use it this way it will assume the value of the current or "previous" state and then the function will execute.

https://reactjs.org/docs/state-and-lifecycle.html#state-updates-may-be-asynchronous