I've created a menu ponent and I'm trying to use the useState hook to store which sub-menus are open. When the menu is closed (from the parent using props) I want to close all sub-menus and to do this I've using the usePrevious hook from the react-hanger library to determine when the main menu is going from OPEN > CLOSED . Here is my code.

import React, { useState } from 'react';
import { usePrevious } from "react-hanger"

const defaultMenusOpen = {menu1:false, menu2:false}

function Menu(props) {

    const [subMenusOpen, setSubMenusOpen] = useState(defaultMenusOpen))
    const prevIsOpen = usePrevious(props.isOpen);


    if(props.isOpen === false && prevIsOpen === true){
        setSubMenusOpen(defaultMenusOpen)
    }

    return (
        {props.isOpen && 
            ... JSX
        }
    );

}

export default Menu

The problem is that this is causing an infinite loop error and continually re-rendering the Menu.

This seems to be because he if statement if TRUE on every re-render because calling setSubMenusOpen doesn't seem to cause usePrevious to store the new value again. This is what I think is happening.

• props.isOpen changes from TRUE > FALSE
• prevIsOpen and props.isOpen are TRUE and FALSE at this point, so...
• setSubMenusOpen() is called which causes a re-render.
• Instead of previsOpen and props.isOpen now being FALSE and FALSE, they remain unchanged, so setSubMenusOpen gets called again, ad finitum

Any help would be greatly appreciated.

I've created a menu ponent and I'm trying to use the useState hook to store which sub-menus are open. When the menu is closed (from the parent using props) I want to close all sub-menus and to do this I've using the usePrevious hook from the react-hanger library to determine when the main menu is going from OPEN > CLOSED . Here is my code.

import React, { useState } from 'react';
import { usePrevious } from "react-hanger"

const defaultMenusOpen = {menu1:false, menu2:false}

function Menu(props) {

    const [subMenusOpen, setSubMenusOpen] = useState(defaultMenusOpen))
    const prevIsOpen = usePrevious(props.isOpen);


    if(props.isOpen === false && prevIsOpen === true){
        setSubMenusOpen(defaultMenusOpen)
    }

    return (
        {props.isOpen && 
            ... JSX
        }
    );

}

export default Menu

The problem is that this is causing an infinite loop error and continually re-rendering the Menu.

This seems to be because he if statement if TRUE on every re-render because calling setSubMenusOpen doesn't seem to cause usePrevious to store the new value again. This is what I think is happening.

• props.isOpen changes from TRUE > FALSE
• prevIsOpen and props.isOpen are TRUE and FALSE at this point, so...
• setSubMenusOpen() is called which causes a re-render.
• Instead of previsOpen and props.isOpen now being FALSE and FALSE, they remain unchanged, so setSubMenusOpen gets called again, ad finitum

Any help would be greatly appreciated.

• javascript
• reactjs
• react-hooks

1 Answer 1

Problem is that you are setting state directly in render which is causing an infinite cycle of setting state and re-rendering. Instead use the useEffect hook and execute it only on isOpen prop change

function Menu(props) {

    const [subMenusOpen, setSubMenusOpen] = useState(defaultMenusOpen))
    const prevIsOpen = usePrevious(props.isOpen);

    useEffect(() => {
        if(props.isOpen === false && prevIsOpen === true){
            setSubMenusOpen(defaultMenusOpen)
        }
    }, [props.isOpen])


    return (
        {props.isOpen && 
            ... JSX
        }
    );

}

export default Menu