I was creating some header for my app, so I tried to place the hooks in some other file for better organization.
But I'm a bit confused, how do I call this function useHeaderNavStatus() when I click the button in the header tag, without creating another useEffect and useState in Header component? Is it possible or I'm too blind?
I appreciate any help! :D
Here is the file structure:
Header Component
const Header = () => {
const headerNav = useHeaderNavStatus();
return (
<header>
<button
ref={headerNav.toggleRef}
onClick={What do I do here?}>
Menu
</button>
</header>
);
}
Hooks file
import { useEffect, useRef, useState } from 'react';
const useHeaderNavStatus = () => {
// Creating ref for toggle button
const toggleRef = useRef<HTMLButtonElement>(null);
// Creating state to know if nav is showing or not
const [isActive, setIsActive] = useState(false);
// This function opens and closes nav
const updateBodyScroll = () => {
setIsActive(!isActive);
const body = document.body.classList;
if (isActive) {
body.remove('no-scroll');
} else {
body.add('no-scroll');
}
};
// This function closes the nav on outside click
const closeNavOnOutsideClick = (event: MouseEvent) => {
if (!toggleRef.current?.contains(event.target as Node))
updateBodyScroll();
};
// Adds and removes event listener to know the target click
useEffect(() => {
if (isActive) {
window.addEventListener('mousedown', closeNavOnOutsideClick);
return () =>
window.removeEventListener('mousedown', closeNavOnOutsideClick);
}
});
return { toggleRef, isActive };
};
Your hook should also return a function that opens the nav:
const openNav = () => setIsActive(true);
return { toggleRef, isActive, openNav };
And then use it:
const Header = () => {
const headerNav = useHeaderNavStatus();
return (
<header>
<button
ref={headerNav.toggleRef}
onClick={headerNav.openNav}>
Menu
</button>
</header>
);
}
According to the docs:
componentDidUpdate() is invoked immediately after updating occurs. This method is not called for the initial render.
We can use the new useEffect() hook to simulate componentDidUpdate(), but it seems like useEffect() is being ran after every render, even the first time. How do I get it to not run on initial render?
As you can see in the example below, componentDidUpdateFunction is printed during the initial render but componentDidUpdateClass was not printed during the initial render.
function ComponentDidUpdateFunction() {
const [count, setCount] = React.useState(0);
React.useEffect(() => {
console.log("componentDidUpdateFunction");
});
return (
<div>
<p>componentDidUpdateFunction: {count} times</p>
<button
onClick={() => {
setCount(count + 1);
}}
>
Click Me
</button>
</div>
);
}
class ComponentDidUpdateClass extends React.Component {
constructor(props) {
super(props);
this.state = {
count: 0,
};
}
componentDidUpdate() {
console.log("componentDidUpdateClass");
}
render() {
return (
<div>
<p>componentDidUpdateClass: {this.state.count} times</p>
<button
onClick={() => {
this.setState({ count: this.state.count + 1 });
}}
>
Click Me
</button>
</div>
);
}
}
ReactDOM.render(
<div>
<ComponentDidUpdateFunction />
<ComponentDidUpdateClass />
</div>,
document.querySelector("#app")
);
<script src="https://unpkg.com/react#16.7.0-alpha.0/umd/react.development.js"></script>
<script src="https://unpkg.com/react-dom#16.7.0-alpha.0/umd/react-dom.development.js"></script>
<div id="app"></div>
We can use the useRef hook to store any mutable value we like, so we could use that to keep track of if it's the first time the useEffect function is being run.
If we want the effect to run in the same phase that componentDidUpdate does, we can use useLayoutEffect instead.
Example
const { useState, useRef, useLayoutEffect } = React;
function ComponentDidUpdateFunction() {
const [count, setCount] = useState(0);
const firstUpdate = useRef(true);
useLayoutEffect(() => {
if (firstUpdate.current) {
firstUpdate.current = false;
return;
}
console.log("componentDidUpdateFunction");
});
return (
<div>
<p>componentDidUpdateFunction: {count} times</p>
<button
onClick={() => {
setCount(count + 1);
}}
>
Click Me
</button>
</div>
);
}
ReactDOM.render(
<ComponentDidUpdateFunction />,
document.getElementById("app")
);
<script src="https://unpkg.com/react#16.7.0-alpha.0/umd/react.development.js"></script>
<script src="https://unpkg.com/react-dom#16.7.0-alpha.0/umd/react-dom.development.js"></script>
<div id="app"></div>
You can turn it into custom hooks, like so:
import React, { useEffect, useRef } from 'react';
const useDidMountEffect = (func, deps) => {
const didMount = useRef(false);
useEffect(() => {
if (didMount.current) func();
else didMount.current = true;
}, deps);
}
export default useDidMountEffect;
Usage example:
import React, { useState, useEffect } from 'react';
import useDidMountEffect from '../path/to/useDidMountEffect';
const MyComponent = (props) => {
const [state, setState] = useState({
key: false
});
useEffect(() => {
// you know what is this, don't you?
}, []);
useDidMountEffect(() => {
// react please run me if 'key' changes, but not on initial render
}, [state.key]);
return (
<div>
...
</div>
);
}
// ...
I made a simple useFirstRender hook to handle cases like focussing a form input:
import { useRef, useEffect } from 'react';
export function useFirstRender() {
const firstRender = useRef(true);
useEffect(() => {
firstRender.current = false;
}, []);
return firstRender.current;
}
It starts out as true, then switches to false in the useEffect, which only runs once, and never again.
In your component, use it:
const firstRender = useFirstRender();
const phoneNumberRef = useRef(null);
useEffect(() => {
if (firstRender || errors.phoneNumber) {
phoneNumberRef.current.focus();
}
}, [firstRender, errors.phoneNumber]);
For your case, you would just use if (!firstRender) { ....
Same approach as Tholle's answer, but using useState instead of useRef.
const [skipCount, setSkipCount] = useState(true);
...
useEffect(() => {
if (skipCount) setSkipCount(false);
if (!skipCount) runYourFunction();
}, [dependencies])
EDIT
While this also works, it involves updating state which will cause your component to re-render. If all your component's useEffect calls (and also all of its children's) have a dependency array, this doesn't matter. But keep in mind that any useEffect without a dependency array (useEffect(() => {...}) will be run again.
Using and updating useRef will not cause any re-renders.
#ravi, yours doesn't call the passed-in unmount function. Here's a version that's a little more complete:
/**
* Identical to React.useEffect, except that it never runs on mount. This is
* the equivalent of the componentDidUpdate lifecycle function.
*
* #param {function:function} effect - A useEffect effect.
* #param {array} [dependencies] - useEffect dependency list.
*/
export const useEffectExceptOnMount = (effect, dependencies) => {
const mounted = React.useRef(false);
React.useEffect(() => {
if (mounted.current) {
const unmount = effect();
return () => unmount && unmount();
} else {
mounted.current = true;
}
}, dependencies);
// Reset on unmount for the next mount.
React.useEffect(() => {
return () => mounted.current = false;
}, []);
};
a simple way is to create a let, out of your component and set in to true.
then say if its true set it to false then return (stop) the useEffect function
like that:
import { useEffect} from 'react';
//your let must be out of component to avoid re-evaluation
let isFirst = true
function App() {
useEffect(() => {
if(isFirst){
isFirst = false
return
}
//your code that don't want to execute at first time
},[])
return (
<div>
<p>its simple huh...</p>
</div>
);
}
its Similar to #Carmine Tambasciabs solution but without using state :)
function useEffectAfterMount(effect, deps) {
const isMounted = useRef(false);
useEffect(() => {
if (isMounted.current) return effect();
else isMounted.current = true;
}, deps);
// reset on unmount; in React 18, components can mount again
useEffect(() => {
isMounted.current = false;
});
}
We need to return what comes back from effect(), because it might be a cleanup function. But we don't need to determine if it is or not. Just pass it on and let useEffect figure it out.
In an earlier version of this post I said resetting the ref (isMounted.current = false) wasn't necessary. But in React 18 it is, because components can remount with their previous state (thanks #Whatabrain).
I thought creating a custom hook would be overkill and I didn't want to muddle my component's readability by using the useLayoutEffect hook for something unrelated to layouts, so, in my case, I simply checked to see if the value of my stateful variable selectedItem that triggers the useEffect callback is its original value in order to determine if it's the initial render:
export default function MyComponent(props) {
const [selectedItem, setSelectedItem] = useState(null);
useEffect(() => {
if(!selectedItem) return; // If selected item is its initial value (null), don't continue
//... This will not happen on initial render
}, [selectedItem]);
// ...
}
This is the best implementation I've created so far using typescript. Basically, the idea is the same, using the Ref but I'm also considering the callback returned by useEffect to perform cleanup on component unmount.
import {
useRef,
EffectCallback,
DependencyList,
useEffect
} from 'react';
/**
* #param effect
* #param dependencies
*
*/
export default function useNoInitialEffect(
effect: EffectCallback,
dependencies?: DependencyList
) {
//Preserving the true by default as initial render cycle
const initialRender = useRef(true);
useEffect(() => {
let effectReturns: void | (() => void) = () => {};
// Updating the ref to false on the first render, causing
// subsequent render to execute the effect
if (initialRender.current) {
initialRender.current = false;
} else {
effectReturns = effect();
}
// Preserving and allowing the Destructor returned by the effect
// to execute on component unmount and perform cleanup if
// required.
if (effectReturns && typeof effectReturns === 'function') {
return effectReturns;
}
return undefined;
}, dependencies);
}
You can simply use it, as usual as you use the useEffect hook but this time, it won't run on the initial render. Here is how you can use this hook.
useNoInitialEffect(() => {
// perform something, returning callback is supported
}, [a, b]);
If you use ESLint and want to use the react-hooks/exhaustive-deps rule for this custom hook:
{
"rules": {
// ...
"react-hooks/exhaustive-deps": ["warn", {
"additionalHooks": "useNoInitialEffect"
}]
}
}
#MehdiDehghani, your solution work perfectly fine, one addition you have to do is on unmount, reset the didMount.current value to false. When to try to use this custom hook somewhere else, you don't get cache value.
import React, { useEffect, useRef } from 'react';
const useDidMountEffect = (func, deps) => {
const didMount = useRef(false);
useEffect(() => {
let unmount;
if (didMount.current) unmount = func();
else didMount.current = true;
return () => {
didMount.current = false;
unmount && unmount();
}
}, deps);
}
export default useDidMountEffect;
Simplified implementation
import { useRef, useEffect } from 'react';
function MyComp(props) {
const firstRender = useRef(true);
useEffect(() => {
if (firstRender.current) {
firstRender.current = false;
} else {
myProp = 'some val';
};
}, [props.myProp])
return (
<div>
...
</div>
)
}
You can use custom hook to run use effect after mount.
const useEffectAfterMount = (cb, dependencies) => {
const mounted = useRef(true);
useEffect(() => {
if (!mounted.current) {
return cb();
}
mounted.current = false;
}, dependencies); // eslint-disable-line react-hooks/exhaustive-deps
};
Here is the typescript version:
const useEffectAfterMount = (cb: EffectCallback, dependencies: DependencyList | undefined) => {
const mounted = useRef(true);
useEffect(() => {
if (!mounted.current) {
return cb();
}
mounted.current = false;
}, dependencies); // eslint-disable-line react-hooks/exhaustive-deps
};
For people who are having trouble with React 18 strict mode calling the useeffect on the initial render twice, try this:
// The init variable is necessary if your state is an object/array, because the == operator compares the references, not the actual values.
const init = [];
const [state, setState] = useState(init);
const dummyState = useRef(init);
useEffect(() => {
// Compare the old state with the new state
if (dummyState.current == state) {
// This means that the component is mounting
} else {
// This means that the component updated.
dummyState.current = state;
}
}, [state]);
Works in development mode...
function App() {
const init = [];
const [state, setState] = React.useState(init);
const dummyState = React.useRef(init);
React.useEffect(() => {
if (dummyState.current == state) {
console.log('mount');
} else {
console.log('update');
dummyState.current = state;
}
}, [state]);
return (
<button onClick={() => setState([...state, Math.random()])}>Update state </button>
);
}
ReactDOM.createRoot(document.getElementById("app")).render(
<React.StrictMode>
<App />
</React.StrictMode>
);
<script crossorigin src="https://unpkg.com/react#18/umd/react.development.js"></script>
<script crossorigin src="https://unpkg.com/react-dom#18/umd/react-dom.development.js"></script>
<div id="app"></div>
And in production.
function App() {
const init = [];
const [state, setState] = React.useState(init);
const dummyState = React.useRef(init);
React.useEffect(() => {
if (dummyState.current == state) {
console.log('mount');
} else {
console.log('update');
dummyState.current = state;
}
}, [state]);
return (
<button onClick={() => setState([...state, Math.random()])}>Update state </button>
);
}
ReactDOM.createRoot(document.getElementById("app")).render(
<React.StrictMode>
<App />
</React.StrictMode>
);
<script crossorigin src="https://unpkg.com/react#18/umd/react.production.min.js"></script>
<script crossorigin src="https://unpkg.com/react-dom#18/umd/react-dom.production.min.js"></script>
<div id="app"></div>
If you want to skip the first render, you can create a state "firstRenderDone" and set it to true in the useEffect with empty dependecy list (that works like a didMount). Then, in your other useEffect, you can check if the first render was already done before doing something.
const [firstRenderDone, setFirstRenderDone] = useState(false);
//useEffect with empty dependecy list (that works like a componentDidMount)
useEffect(() => {
setFirstRenderDone(true);
}, []);
// your other useEffect (that works as componetDidUpdate)
useEffect(() => {
if(firstRenderDone){
console.log("componentDidUpdateFunction");
}
}, [firstRenderDone]);
All previous are good, but this can be achieved in a simplier way considering that the action in useEffect can be "skipped" placing an if condition(or any other ) that is basically not run first time, and still with the dependency.
For example I had the case of :
Load data from an API but my title has to be "Loading" till the date were not there, so I have an array, tours that is empty at beginning and show the text "Showing"
Have a component rendered with different information from those API.
The user can delete one by one those info, even all making the tour array empty again as the beginning but this time the API fetch is been already done
Once the tour list is empty by deleting then show another title.
so my "solution" was to create another useState to create a boolean value that change only after the data fetch making another condition in useEffect true in order to run another function that also depend on the tour length.
useEffect(() => {
if (isTitle) {
changeTitle(newTitle)
}else{
isSetTitle(true)
}
}, [tours])
here my App.js
import React, { useState, useEffect } from 'react'
import Loading from './Loading'
import Tours from './Tours'
const url = 'API url'
let newTours
function App() {
const [loading, setLoading ] = useState(true)
const [tours, setTours] = useState([])
const [isTitle, isSetTitle] = useState(false)
const [title, setTitle] = useState("Our Tours")
const newTitle = "Tours are empty"
const removeTours = (id) => {
newTours = tours.filter(tour => ( tour.id !== id))
return setTours(newTours)
}
const changeTitle = (title) =>{
if(tours.length === 0 && loading === false){
setTitle(title)
}
}
const fetchTours = async () => {
setLoading(true)
try {
const response = await fetch(url)
const tours = await response.json()
setLoading(false)
setTours(tours)
}catch(error) {
setLoading(false)
console.log(error)
}
}
useEffect(()=>{
fetchTours()
},[])
useEffect(() => {
if (isTitle) {
changeTitle(newTitle)
}else{
isSetTitle(true)
}
}, [tours])
if(loading){
return (
<main>
<Loading />
</main>
)
}else{
return (
<main>
<Tours tours={tours} title={title} changeTitle={changeTitle}
removeTours={removeTours} />
</main>
)
}
}
export default App
const [dojob, setDojob] = useState(false);
yourfunction(){
setDojob(true);
}
useEffect(()=>{
if(dojob){
yourfunction();
setDojob(false);
}
},[dojob]);
I've got some components which need to render sequentially once they've loaded or marked themselves as ready for whatever reason.
In a typical {things.map(thing => <Thing {...thing} />} example, they all render at the same time, but I want to render them one by one I created a hook to to provide a list which only contains the sequentially ready items to render.
The problem I'm having is that the children need a function in order to tell the hook when to add the next one into its ready to render state. This function ends up getting changed each time and as such causes an infinite number of re-renders on the child components.
In the examples below, the child component useEffect must rely on the dependency done to pass the linter rules- if i remove this it works as expected because done isn't a concern whenever it changes but obviously that doesn't solve the issue.
Similarly I could add if (!attachment.__loaded) { into the child component but then the API is poor for the hook if the children need specific implementation such as this.
I think what I need is a way to stop the function being recreated each time but I've not worked out how to do this.
Codesandbox link
useSequentialRenderer.js
import { useReducer, useEffect } from "react";
const loadedProperty = "__loaded";
const reducer = (state, {i, type}) => {
switch (type) {
case "ready":
const copy = [...state];
copy[i][loadedProperty] = true;
return copy;
default:
return state;
}
};
const defaults = {};
export const useSequentialRenderer = (input, options = defaults) => {
const [state, dispatch] = useReducer(options.reducer || reducer, input);
const index = state.findIndex(a => !a[loadedProperty]);
const sliced = index < 0 ? state.slice() : state.slice(0, index + 1);
const items = sliced.map((item, i) => {
function done() {
dispatch({ type: "ready", i });
return i;
}
return { ...item, done };
});
return { items };
};
example.js
import React, { useEffect, useState } from "react";
import ReactDOM from "react-dom";
import { useSequentialRenderer } from "./useSequentialRenderer";
const Attachment = ({ children, done }) => {
const [loaded, setLoaded] = useState(false);
useEffect(() => {
const delay = Math.random() * 3000;
const timer = setTimeout(() => {
setLoaded(true);
const i = done();
console.log("happening multiple times", i, new Date());
}, delay);
return () => clearTimeout(timer);
}, [done]);
return <div>{loaded ? children : "loading"}</div>;
};
const Attachments = props => {
const { items } = useSequentialRenderer(props.children);
return (
<>
{items.map((attachment, i) => {
return (
<Attachment key={attachment.text} done={() => attachment.done()}>
{attachment.text}
</Attachment>
);
})}
</>
);
};
function App() {
const attachments = [1, 2, 3, 4, 5, 6, 7, 8].map(a => ({
loaded: false,
text: a
}));
return (
<div className="App">
<Attachments>{attachments}</Attachments>
</div>
);
}
const rootElement = document.getElementById("root");
ReactDOM.render(<App />, rootElement);
Wrap your callback in an aditional layer of dependency check with useCallback. This will ensure a stable identity across renders
const Component = ({ callback }) =>{
const stableCb = useCallback(callback, [])
useEffect(() =>{
stableCb()
},[stableCb])
}
Notice that if the signature needs to change you should declare the dependencies as well
const Component = ({ cb, deps }) =>{
const stableCb = useCallback(cb, [deps])
/*...*/
}
Updated Example:
https://codesandbox.io/s/wizardly-dust-fvxsl
Check if(!loaded){.... setTimeout
or
useEffect with [loaded]);
useEffect(() => {
const delay = Math.random() * 1000;
const timer = setTimeout(() => {
setLoaded(true);
const i = done();
console.log("rendering multiple times", i, new Date());
}, delay);
return () => clearTimeout(timer);
}, [loaded]);
return <div>{loaded ? children : "loading"}</div>;
};
I am trying to build Hanging man game and want to get value from useState inside the checkMatchLetter function, but not sure if that is possible and what I did wrong....
import React, { useState, useEffect } from 'react';
import { fetchButton } from '../actions';
import axios from 'axios';
import 'babel-polyfill';
const App = () => {
const [word, setWord] = useState([]);
const [underscore, setUnderscore] = useState([]);
const [data, setData] = useState([]);
useEffect(() => {
const runEffect = async () => {
const result = await axios('src/api/api.js');
setData(result.data)
}
runEffect();
}, []);
const randomWord = () => {
const chosenWord = data[Math.floor(Math.random() * data.length)];
replaceLetter(chosenWord.word);
}
const replaceLetter = (string) => {
let getString = string; // here it shows a valid string.
setWord(getString);
let stringToUnderScore = getString.replace(/[a-z]/gi, '_');
setUnderscore(stringToUnderScore);
}
useEffect(() => {
const checkLetter = (event) => {
if(event.keyCode >= 65 && event.keyCode <= 90) {
checkMatchLetter(word, String.fromCharCode(event.keyCode).toLowerCase());
}
};
document.addEventListener('keydown', checkLetter);
return () => {
document.removeEventListener('keydown', checkLetter);
}
}, []);
const checkMatchLetter = (keyButton) => {
console.log(keyButton);
let wordLength = word.length;
console.log(wordLength); // here it outputs '0'
/// here I want word of useState here....
}
return (
<div>
<p>{word}</p>
<p>{underscore}</p>
<button onClick={randomWord}></button>
</div>
)
}
export default App;
The reason why I want to obtain that value inside this function is so I can compare the clicked keybutton (a-z) to the current chosenword. And if there is something wrong with other functions, please feel free to share your feedback here below as well.
You're using a variable defined inside the component render function in a useEffect effect and that variable is missing in the hook's deps. Always include the deps you need (I highly recommend the lint rule react-hooks/exhaustive-deps). When you add checkMatchLetter to deps you'll always have the newest instance of the function inside your effect instead of always using the old version from the first render like you do now.
useEffect(() => {
const checkLetter = (event) => {
if(event.keyCode >= 65 && event.keyCode <= 90) {
checkMatchLetter(word, String.fromCharCode(event.keyCode).toLowerCase());
}
};
document.addEventListener('keydown', checkLetter);
return () => {
document.removeEventListener('keydown', checkLetter);
}
}, [checkMatchLetter, word]);
This change will make the effect run on every render. To rectify that, you can memoise your callbacks. However, that's a new can of worms.