React useEffect Guides
The useEffect Hook lets you perform side effects in your components.
This is a collection of top and trending guides written by the community on subjects related to React useEffect concepts. For all things React, check out the React tag! Please contribute more posts like this to help your fellow developer in need.
The useEffect hook is built in a way that if we return a function within the method, this function will execute when the component gets disassociated. This is very useful because we can use it to remove unnecessary behavior or prevent memory leaking issues.
A hook is a function which enables you use state and other react features without writing ES6 classes.
useEffecthook is part of the react hooks API. If you are familiar with react life cycles,
useEffecthook is equivalent to life cycle methods
componentWillUnmountcombined. In fact, according to the React documentation on Hooks,
useEffecthook was developed to address some of the challenges posed by life cycle methods of ES6 class components. Since this post is about what effect hook is and how it is used, i won't go into why it was developed. You can look at it Here.
In React functional components, we perform
side effectssuch as fetching data from an API or manually updating the DOM inside the
In React, side effects can be handled in functional components using
useEffecthook. In this post, I'm going to talk about the dependency array which holds our props/state and specifically what happens in case there's an object in this array.
useEffecthook is a great way to wrap side effects since the release of React 16.8. To quickly recap, this hook allows you to create functional components with behaviour akin to React classes'
There is a way to use
useEffectto only run when variables provided in a second argument are updated, like this:
Whenever we need to make use of side effects in our application,
That's exactly what I have found recently.
Let's say we have a parent and a child and we pass
setStatefunction to the child in order to it can set state for parent from within a
useEffecthook inside child component. This scenario will cause an infinite loop no matter what you put in the dependencies' second argument array of
Let's say what in my opinion happens.
setStatecauses the parent to re-render because we are updating its state. But this implies a render of the child. And I say render and not re-render because when parent re-renders, for
useEffecthook is like rendering of the child was first render, and that's why no matter what you put on the dependencies array it will always execute its side effect, setting state for parent and initiating a new loop, that will continue forever.
So when you lift the state up in React.js you must take care not to call
dispatch(this applies as well to
useReducer) inside a
useEffecthook from within a child component.
Here, I show you the code:
But Now each time when any of state is updated, this hook method is calling.
but we need to call this only at component will mount and unmount. So how can we fix it?
Simply, you can pass the empty array as a second argument. By doing this, this useEffect will call only at the component mount and unmount.
Fetching API data with useEffect can be tricky sometimes. In this article, we will look at one trick for efficient data fetching with useEffect.
Even if the component is unmounted, useEffect will try to maintain contact with your data-fetching function. Because this is an anti-pattern that exposes your app to memory leaks, canceling your useEffect subscription optimizes your app.
Before React 16.8, we were forced to use the class-based component to have access in component lifecycle. And now with Hooks, we are now able to use functional component for state management, data fetching etc. We can now replace component lifecycle like
useEffectin our React component.
componentWillUnmountlifecycle methods. This is very useful for the following reasons: it reduces the amount of code, simplifies the code and allows for multiple
useEffecthooks to be called in a single component.
While all these are beautiful, there is a little caveat (or maybe not) that is a little bit frustrating when working with useEffect hook.
If you want to see the issue, comment out the useEffect hook and you will see that it fades out, then comes right back into view!
"ESLint: React Hook useEffect has missing dependencies: 'body', 'dispatch', 'headers', 'method', 'url', and 'user.jwt'. Either include them or remove the dependency array.(react-hooks/exhaustive-deps)"
I've put all data fetching in
useEffecthook - pretty standard approach. However,
useEffectdoes not play very well with server-side rendering. I've managed to work this out by creating custom hook
useSSE- "use server-side effect" and I've created an npm package from it.
I'm using the OpenWeather REST API which comes in JSON format. I know I have to make my fetch,(Axios in my case) call inside the useEffect because the component needs to render first, then calls the REST endpoint.
If you haven’t learned Hooks yet, you should do it as soon as possible. And if you’ve been reading about them, you may be a bit confused about the useEffect Hook 😕
The callback we give to
useStateupdater function when data is ready — updating our component.
The useEffect hook is the combination of componentDidMount(run only once when the component is inserted into the DOM tree structure) componentDidUpdate(run something on each render), and componentWillUnmount (run when the component will be removed from the DOM tree) class lifecycle methods.
Using useEffect Hook, tells React that your component needs to do something after render. React will remember the function you passed and call it later after performing the DOM updates.
The code behind it is very simple. It only takes a
useRef, to keep track of the initial render, and a useEffect with a guard to check whether if it's the first mount or not:
As we know, use effect is basically used to perform side Effect (API request). So it's obvious that we will make our API request in the useEffect function.
The useEffect hook receives two parameters: one function to be executed and an array of dependencies.
I started exploring react's functional component and really like how it has made the code neat and compressed the component to a few lines. We are going to discuss 3 most used scenarios there must be more where you can make use of
useEffecthook. In this article, I'll be comparing
useEffectwith classical component hooks and explaining the whys and hows. So yeah here's the list of use cases.
The Hooks API is a great feature that was added in version v16.8 last february and change the way on how we write our React Apps. We now write more functional components instead of class components. We don't need to bind any more functions inside the constructor because of the functional components. So today we demystify the useEffect API.
Gladly, I understood it, and I now want to show you what useEffect is and how you can use it.
If you have just started working on React or have ever written a functional component, I am pretty sure that you may have come across useEffect hook and you may know that it is used to perform some side effects like data fetching, sending HTTP requests, etc. But in this post we will talk about another react hook called useLayoutEffect and see how it is different from useEffect hook.
Docs are boring, let's build a movie finder app to learn React hooks (useReducer, useEffect and useContext)
The useEffect hook takes two arguments:
Now I want to share my mental model in this small cheat sheet to help you learn
useEffectbetter or own a better mental model.
UseEffect? What is syntax ? How does it work? When to use it ? And Some common use cases of useEffect Hook.
If you want to run an effect and clean it up only once (on mount and unmount), you can pass an empty array () as a second argument. This tells React that your effect doesn’t depend on any values from props or state, so it never needs to re-run. This isn’t handled as a special case — it follows directly from how the dependencies array always works.
If you pass an empty array (), the props and state inside the effect will always have their initial values. While passing  as the second argument is closer to the familiar componentDidMount and componentWillUnmount mental model, there are usually better solutions to avoid re-running effects too often. Also, don’t forget that React defers running useEffect until after the browser has painted, so doing extra work is less of a problem.
useEffectis an alternative to the "old"
React's useEffect hook is a super hook to run side effects.
You might be wondering what kind of side effects we could be talking about?
When building a React app, there will be times where we want to run a piece of code after a component is rendered (think fetching data from an api as one example) — the useEffect React Hook will help us accomplish that.
useEffectes quizá el hook que más confusiones genera a la hora de utilizarlo.
Algunas de esas confusiones se debe al intento de comparar su funcionamiento con los estados del ciclo de vida de un componente de clase, algo que aclaro en este post anterior
useEffecthook is used quite often in applications. It is used to perform side effects in your components like subscribing/unsubscribing to events, making API requests etc.
O React consegue fazer isso acompanhando cada componente e a ordem em que cada hook é declarado. Essa é a razão pela qual você não pode ter um React Hook dentro de uma condicional. Se useState, useEffect ou qualquer outro hook for criado condicionalmente , o React não poderá controlá-lo adequadamente.
Another fix is to use an AbortController to terminate the request from the first useEffect . Let’s say this is your code:
"If you’re familiar with React class lifecycle methods, you can think of useEffect Hook as componentDidMount, componentDidUpdate, and componentWillUnmount combined."
Why should I use useEffect when console.log even it works well without, after rendering?
I was working on a project and I had to close out some modals, and realized there were both Class component modals and Functional component modals that were involved... so I decided for the class component I would use the life cycle methods and use useEffect for the functional components heres what they look like
When we use effects, or more precisely the
useEffecthook, than because very often we do want to execute something asynchronously. In most scenarios we are doing this when a component gets mounted.
I’ve certainly fallen victim to this many, many times. Particularly with
useEffect. Before we dive into this particular hook, let me say that I love writing React with hooks and wouldn’t want to go back to classes. That said,
useEffectis a big pain point.
Happy React useEffect coding!