I am new to react js and I am having a hard time figuring out how to prevent delay updating of use state from axios response
Here's my code:
First, I declared countUsername as useState
const [countUsername, setUsername] = useState(0);
Second, I created arrow function checking if the username is still available
const checkUser = () => {
RestaurantDataService.checkUsername(user.username)
.then(response => {
setUsername(response.data.length);
})
.catch(e => {
console.log(e);
})
}
So, every time I check the value of countUsername, it has delay like if I trigger the button and run checkUser(), the latest response.data.length won't save.
Scenario if I console.log() countUseranme
I entered username1(not available), the value of countUsername is still 0 because it has default value of 0 then when I trigger the function once again, then that will just be the time that the value will be replaced.
const saveUser = () => {
checkUser();
console.log(countUsername);
}
Is there anything that I have forgot to consider? Thank you
usually there is a delay for every api call, so for that you can consider an state like below:
const [loading,toggleLoading] = useState(false)
beside that you can change arrow function to be async like below:
const checking = async ()=>{
toggleLoading(true);
const res = await RestaurantDataService.checkUsername(user.username);
setUsername(response.data.length);
toggleLoading(false);
}
in the above function you can toggle loading state for spceifing checking state and disable button during that or shwoing spinner in it:
<button onClick={checking } disabled={loading}>Go
i hope this help
.then is not synchronous, it's more of a callback and will get called later when the api finishes. So your console log actually goes first most of the time before the state actually saves. That's not really something you control.
You can do an async / await and return the data if you need to use it right away before the state changes. And I believe the way state works is that it happens after the execution:
"State Updates May Be Asynchronous" so you can't really control when to use it because you can't make it wait.
In my experience you use the data right away from the service and update the state or create a useEffect, i.g., useEffect(() => {}, [user]), to update the page with state.
const checkUser = async () => {
try {
return await RestaurantDataService.checkUsername(user.username);
} catch(e) {
console.log(e);
}
}
const saveUser = async () => {
const user = await checkUser();
// do whatever you want with user
console.log(user);
}
I need to make an api request when a search query param from an input fields changes, but only if the field is not empty.
I am testing with several answers found on this site, but can't get them working
Firstly this one with a custom hook
export function useDebounce(value, delay) {
const [debouncedValue, setDebouncedValue] = useState(value);
useEffect(() => {
const handler = setTimeout(() => {
setDebouncedValue(value);
}, delay);
return () => clearTimeout(handler);
}, [value, delay]);
return debouncedValue;
}
now in my component I do this
const debouncedTest = useDebounce(() => {console.log("something")}, 1000);
but this seems to gets called every rerender regardless of any parameter, and I need to be able to call it inside a useEffect, like this
useEffect(() => {
if (query) {
useDebounce(() => {console.log("something")}, 1000);
} else {
//...
}
}, [query]);
which of course does not work
Another approach using lodash
const throttledTest = useRef(throttle(() => {
console.log("test");
}, 1000, {leading: false}))
But how would i trigger this from the useEffect above? I don't understand how to make this work
Thank you
Your hook's signature is not the same as when you call it.
Perhaps you should do something along these lines:
const [state, setState] = useState(''); // name it whatever makes sense
const debouncedState = useDebounce(state, 1000);
useEffect(() => {
if (debouncedState) functionCall(debouncedState);
}, [debouncedState])
I can quickly point out a thing or two here.
useEffect(() => {
if (query) {
useDebounce(() => {console.log("something")}, 1000);
} else {
//...
}
}, [query]);
technically you can't do the above, useEffect can't be nested.
Normally debounce isn't having anything to do with a hook. Because it's a plain function. So you should first look for a solid debounce, create one or use lodash.debounce. And then structure your code to call debounce(fn). Fn is the original function that you want to defer with.
Also debounce is going to work with cases that changes often, that's why you want to apply debounce to reduce the frequency. Therefore it'll be relatively uncommon to see it inside a useEffect.
const debounced = debounce(fn, ...)
const App = () => {
const onClick = () => { debounced() }
return <button onClick={onClick} />
}
There's another common problem, people might take debounce function inside App. That's not correct either, since the App is triggered every time it renders.
I can provide a relatively more detailed solution later. It'll help if you can explain what you'd like to do as well.
I have a very simple example I wrote in a class component:
setErrorMessage(msg) {
this.setState({error_message: msg}, () => {
setTimeout(() => {
this.setState({error_message: ''})
}, 5000);
});
}
So here I call the setState() method and give it a callback as a second argument.
I wonder if I can do this inside a functional component with the useState hook.
As I know you can not pass a callback to the setState function of this hook. And when I use the useEffect hook - it ends up in an infinite loop:
So I guess - this functionality is not included into functional components?
The callback functionality isn't available in react-hooks, but you can write a simple get around using useEffect and useRef.
const [errorMessage, setErrorMessage] = useState('')
const isChanged = useRef(false);
useEffect(() => {
if(errorMessage) { // Add an existential condition so that useEffect doesn't run for empty message on first rendering
setTimeout(() => {
setErrorMessage('');
}, 5000);
}
}, [isChanged.current]); // Now the mutation will not run unless a re-render happens but setErrorMessage does create a re-render
const addErrorMessage = (msg) => {
setErrorMessage(msg);
isChanged.current = !isChanged.current; // intentionally trigger a change
}
The above example is considering the fact that you might want to set errorMessage from somewhere else too where you wouldn't want to reset it. If however you want to reset the message everytime you setErrorMessage, you can simply write a normal useEffect like
useEffect(() => {
if(errorMessage !== ""){ // This check is very important, without it there will be an infinite loop
setTimeout(() => {
setErrorMessage('');
}, 5000);
}
}, [errorMessage])
I'm using a componentDidUpdate function
componentDidUpdate(prevProps){
if(prevProps.value !== this.props.users){
ipcRenderer.send('userList:store',this.props.users);
}
to this
const users = useSelector(state => state.reddit.users)
useEffect(() => {
console.log('users changed')
console.log({users})
}, [users]);
but it I get the message 'users changed' when I start the app. But the user state HAS NOT changed at all
Yep, that's how useEffect works. It runs after every render by default. If you supply an array as a second parameter, it will run on the first render, but then skip subsequent renders if the specified values have not changed. There is no built in way to skip the first render, since that's a pretty rare case.
If you need the code to have no effect on the very first render, you're going to need to do some extra work. You can use useRef to create a mutable variable, and change it to indicate once the first render is complete. For example:
const isFirstRender = useRef(true);
const users = useSelector(state => state.reddit.users);
useEffect(() => {
if (isFirstRender.current) {
isFirstRender.current = false;
} else {
console.log('users changed')
console.log({users})
}
}, [users]);
If you find yourself doing this a lot, you could create a custom hook so you can reuse it easier. Something like this:
const useUpdateEffect = (callback, dependencies) => {
const isFirstRender = useRef(true);
useEffect(() => {
if (isFirstRender.current) {
isFirstRender.current = false;
} else {
return callback();
}
}, dependencies);
}
// to be used like:
const users = useSelector(state => state.reddit.users);
useUpdateEffect(() => {
console.log('users changed')
console.log({users})
}, [users]);
If you’re familiar with React class lifecycle methods, you can think
of useEffect Hook as componentDidMount, componentDidUpdate, and
componentWillUnmount combined.
As from: Using the Effect Hook
This, it will be invoked as the component is painted in your DOM, which is likely to be closer to componentDidMount.
With React's new Effect Hooks, I can tell React to skip applying an effect if certain values haven't changed between re-renders - Example from React's docs:
useEffect(() => {
document.title = `You clicked ${count} times`;
}, [count]); // Only re-run the effect if count changes
But the example above applies the effect upon initial render, and upon subsequent re-renders where count has changed. How can I tell React to skip the effect on the initial render?
As the guide states,
The Effect Hook, useEffect, adds the ability to perform side effects from a function component. It serves the same purpose as componentDidMount, componentDidUpdate, and componentWillUnmount in React classes, but unified into a single API.
In this example from the guide it's expected that count is 0 only on initial render:
const [count, setCount] = useState(0);
So it will work as componentDidUpdate with additional check:
useEffect(() => {
if (count)
document.title = `You clicked ${count} times`;
}, [count]);
This is basically how custom hook that can be used instead of useEffect may work:
function useDidUpdateEffect(fn, inputs) {
const didMountRef = useRef(false);
useEffect(() => {
if (didMountRef.current) {
return fn();
}
didMountRef.current = true;
}, inputs);
}
Credits go to #Tholle for suggesting useRef instead of setState.
Here's a custom hook that just provides a boolean flag to indicate whether the current render is the first render (when the component was mounted). It's about the same as some of the other answers but you can use the flag in a useEffect or the render function or anywhere else in the component you want. Maybe someone can propose a better name.
import { useRef, useEffect } from 'react';
export const useIsMount = () => {
const isMountRef = useRef(true);
useEffect(() => {
isMountRef.current = false;
}, []);
return isMountRef.current;
};
You can use it like:
import React, { useEffect } from 'react';
import { useIsMount } from './useIsMount';
const MyComponent = () => {
const isMount = useIsMount();
useEffect(() => {
if (isMount) {
console.log('First Render');
} else {
console.log('Subsequent Render');
}
});
return isMount ? <p>First Render</p> : <p>Subsequent Render</p>;
};
And here's a test for it if you're interested:
import { renderHook } from '#testing-library/react-hooks';
import { useIsMount } from '../useIsMount';
describe('useIsMount', () => {
it('should be true on first render and false after', () => {
const { result, rerender } = renderHook(() => useIsMount());
expect(result.current).toEqual(true);
rerender();
expect(result.current).toEqual(false);
rerender();
expect(result.current).toEqual(false);
});
});
Our use case was to hide animated elements if the initial props indicate they should be hidden. On later renders if the props changed, we did want the elements to animate out.
I found a solution that is more simple and has no need to use another hook, but it has drawbacks.
useEffect(() => {
// skip initial render
return () => {
// do something with dependency
}
}, [dependency])
This is just an example that there are others ways of doing it if your case is very simple.
The drawback of doing this is that you can't have a cleanup effect and will only execute when the dependency array changes the second time.
This isn't recommended to use and you should use what the other answers are saying, but I only added this here so people know that there is more than one way of doing this.
Edit:
Just to make it more clear, you shouldn't use this approach to solving the problem in the question (skipping the initial render), this is only for teaching purpose that shows you can do the same thing in different ways.
If you need to skip the initial render, please use the approach on other answers.
I use a regular state variable instead of a ref.
// Initializing didMount as false
const [didMount, setDidMount] = useState(false)
// Setting didMount to true upon mounting
useEffect(() => { setDidMount(true) }, [])
// Now that we have a variable that tells us wether or not the component has
// mounted we can change the behavior of the other effect based on that
const [count, setCount] = useState(0)
useEffect(() => {
if (didMount) document.title = `You clicked ${count} times`
}, [count])
We can refactor the didMount logic as a custom hook like this.
function useDidMount() {
const [didMount, setDidMount] = useState(false)
useEffect(() => { setDidMount(true) }, [])
return didMount
}
Finally, we can use it in our component like this.
const didMount = useDidMount()
const [count, setCount] = useState(0)
useEffect(() => {
if (didMount) document.title = `You clicked ${count} times`
}, [count])
UPDATE Using useRef hook to avoid the extra rerender (Thanks to #TomEsterez for the suggestion)
This time our custom hook returns a function returning our ref's current value. U can use the ref directly too, but I like this better.
function useDidMount() {
const mountRef = useRef(false);
useEffect(() => { mountRef.current = true }, []);
return () => mountRef.current;
}
Usage
const MyComponent = () => {
const didMount = useDidMount();
useEffect(() => {
if (didMount()) // do something
else // do something else
})
return (
<div>something</div>
);
}
On a side note, I've never had to use this hook and there are probably better ways to handle this which would be more aligned with the React programming model.
Let me introduce to you react-use.
npm install react-use
Wanna run:
only after first render? -------> useUpdateEffect
only once? -------> useEffectOnce
check is it first mount? -------> useFirstMountState
Want to run effect with deep compare, shallow compare or throttle? and much more here.
Don't want to install a library? Check the code & copy. (maybe a star for the good folks there too)
Best thing is one less thing for you to maintain.
A TypeScript and CRA friendly hook, replace it with useEffect, this hook works like useEffect but won't be triggered while the first render happens.
import * as React from 'react'
export const useLazyEffect:typeof React.useEffect = (cb, dep) => {
const initializeRef = React.useRef<boolean>(false)
React.useEffect((...args) => {
if (initializeRef.current) {
cb(...args)
} else {
initializeRef.current = true
}
// eslint-disable-next-line react-hooks/exhaustive-deps
}, dep)
}
Here is my implementation based on Estus Flask's answer written in Typescript. It also supports cleanup callback.
import { DependencyList, EffectCallback, useEffect, useRef } from 'react';
export function useDidUpdateEffect(
effect: EffectCallback,
deps?: DependencyList
) {
// a flag to check if the component did mount (first render's passed)
// it's unrelated to the rendering process so we don't useState here
const didMountRef = useRef(false);
// effect callback runs when the dependency array changes, it also runs
// after the component mounted for the first time.
useEffect(() => {
// if so, mark the component as mounted and skip the first effect call
if (!didMountRef.current) {
didMountRef.current = true;
} else {
// subsequent useEffect callback invocations will execute the effect as normal
return effect();
}
}, deps);
}
Live Demo
The live demo below demonstrates the different between useEffect and useDidUpdateEffect hooks
I was going to comment on the currently accepted answer, but ran out of space!
Firstly, it's important to move away from thinking in terms of lifecycle events when using functional components. Think in terms of prop/state changes. I had a similar situation where I only wanted a particular useEffect function to fire when a particular prop (parentValue in my case) changes from its initial state. So, I created a ref that was based on its initial value:
const parentValueRef = useRef(parentValue);
and then included the following at the start of the useEffect fn:
if (parentValue === parentValueRef.current) return;
parentValueRef.current = parentValue;
(Basically, don't run the effect if parentValue hasn't changed. Update the ref if it has changed, ready for the next check, and continue to run the effect)
So, although other solutions suggested will solve the particular use-case you've provided, it will help in the long run to change how you think in relation to functional components.
Think of them as primarily rendering a component based on some props.
If you genuinely need some local state, then useState will provide that, but don't assume your problem will be solved by storing local state.
If you have some code that will alter your props during a render, this 'side-effect' needs to be wrapped in a useEffect, but the purpose of this is to have a clean render that isn't affected by something changing as it's rendering. The useEffect hook will be run after the render has completed and, as you've pointed out, it's run with every render - unless the second parameter is used to supply a list of props/states to identify what changed items will cause it to be run subsequent times.
Good luck on your journey to Functional Components / Hooks! Sometimes it's necessary to unlearn something to get to grips with a new way of doing things :)
This is an excellent primer: https://overreacted.io/a-complete-guide-to-useeffect/
Below solution is similar to above, just a little cleaner way i prefer.
const [isMount, setIsMount] = useState(true);
useEffect(()=>{
if(isMount){
setIsMount(false);
return;
}
//Do anything here for 2nd render onwards
}, [args])
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
};
Example:
useEffectAfterMount(() => {
document.title = `You clicked ${count} times`;
}, [count])