useState or const: what's the difference?

#react #discuss

Here's a quick bite for you. What are the differences between these two declarations?

const Tuesday = () => {
  const [needsTacos] = React.useState(true); // 1
  const needsTacos = true; // 2
  return <marquee>Of course we need tacos!</marquee>
}

Top comments (9)

Sung M. Kim • Sep 10 '19

// 1. needsTacos "can" trigger re-render.
// 2. needsTacos doesn't trigger re-render (same goes for ref by useRef)

Ryan Penchenski • Sep 10 '19

Wouldn't you need a "setNeedsTacos" to trigger a re-render?

Sung M. Kim • Sep 10 '19

Yes, you are right, Ryan.

Updating the state using setNeedsTacos "can" cause the re-render.

Robert Valenzuela • Mar 25 '21

thx this help me to understand the difference

DeChamp • Sep 10 '19 • Edited

I'll bite... useState should be used with [needsTacos, setNeedsTacos] first off... since the whole purpose is to be able to manage the state. One is a constant value which never changes. So I feel like this is a trick question or I totally misunderstood it.

Jesse M. Holmes • Sep 10 '19

Right? I havent found a reason to use

const [variableOnly] = useState()

 const [,setterOnly] = useState()

I just thought it was a fun thinking exercise.

DeChamp • Sep 10 '19

It is a fun thinking exercise, because I was racking my brain to see if i was missing something. It also leads in to letting others know that, yes you may think it's an option, but it's not the proper use. So maybe someone will see this and have the questions answered. Thumbs up!

Emmanuel Barrera • Sep 11 '19

I think you dont know how use hooks so... the hook are only like observables, and that's the way that are const because its just variables where i will push and pull values...

And like observables that variables have triggers that will be dispatched and make renders or active useEffects ( or more hooks ) because all the hook are like functions that are attached with observables, so the hook are just triggers attached to observables

so... i dont know why you have only the observables and not have the function to change that observable value, if you only wants to keep the values saved, you just need to have the const ( like the functions, because you dont need change the function value (i hope.. for the best practices be with you... xd))