CODEWITHSUNDEEP
javascriptreactjs
jok
jok

Reputation: 283

Why does the setState fn needs to be called through another function?

Lets look at the code below

import React from "react"

export default function App() {
    const [isGoingOut, setGoingOut] = React.useState(false);
    
    function yeet() {
        setGoingOut(prevValue => prevValue ? false : true);    
    }
    
    return (
        <div className="state">
            <h1 className="state--title">Do I feel like going out tonight?</h1>
            <div className="state--value" onClick={yeet}>
                <h1>{isGoingOut ? "Yes" : "No"}</h1>
            </div>
        </div>
    )
}

I'm calling the set function setGoingOut() through the function yeet(). However, if I directly call the setGoingOut() function as below

import React from "react"

export default function App() {
    const [isGoingOut, setGoingOut] = React.useState(false);
    
    setGoingOut(prevValue => prevValue ? false : true);
    
    return (
        <div className="state">
            <h1 className="state--title">Do I feel like going out tonight?</h1>
            <div className="state--value" onClick={setGoingOut}>
                <h1>{isGoingOut ? "Yes" : "No"}</h1>
            </div>
        </div>
    )
}

it throws an error. Is this related to the React philosophy of not letting the state be changed directly (the same reason we can't change a state variable count as count++ but have to do count + 1?

Upvotes: 2

Views: 149

Answers (1)

DecPK
DecPK

Reputation: 25398

In the first code snippet, you are calling yeet which inside change isGoingOut using setGoingOut. This will surely works

function yeet() {
  setGoingOut((prevValue) => (prevValue ? false : true));
}

In the second snippet, you are changing state directly which will create infinite loop and produces error as:

Too many re-renders. React limits the number of renders to prevent an infinite loop.

You should change state not every time, but only when user clicks the button

setGoingOut(prevValue => prevValue ? false : true);

But, If you are trying to call directly setGoingOut then what it will do is:

  1. Pass event object to setGoingOut which will become value of isGoingOut and then you can't change its value because you are setting the state of isGoingOut as a new event object particularly SyntheticEvent that React send as an argument.

    onClick={setGoingOut}

This is not the way you should change state.

You can change state on click as:

<div
  className="state--value"
  onClick={() => setGoingOut((prevValue) => (prevValue ? false : true))}>
  <h1>{isGoingOut ? "Yes" : "No"}</h1>
</div>

Upvotes: 1

Related Questions