useEffect - Fullstackadda

useEffect is a hook in React that allows you to perform side effects in functional components. It is a way to use lifecycle methods, such as componentDidMount, componentDidUpdate, and componentWillUnmount, in functional components.

Here is an example of using the useEffect hook to fetch data from an API and update the component state:

import { useState, useEffect } from 'react'

function Example() {
  const [data, setData] = useState(null)

  useEffect(() => {
    fetch('https://my-api.com/data')
      .then(response => response.json())
      .then(data => setData(data))
  }, [])

  return (
    <div>
      {data ? <p>{data.name}</p> : <p>Loading...</p>}
    </div>
  )
}

In this example, the useEffect hook is called with a function that fetches data from an API and updates the component state with the setData function. The empty array as the second argument tells React to only run the effect when the component mounts, similar to componentDidMount.

The useEffect hook can be called multiple times in a single component to perform different side effects. It is a very useful and powerful way to add lifecycle methods to functional components in React.

Here is an example of using the useEffect hook to perform a side effect in a functional component:

import { useState, useEffect } from 'react'

function Example() {
  const [count, setCount] = useState(0)

  useEffect(() => {
    document.title = `You clicked ${count} times`
  }, [count])

  return (
    <div>
      <p>You clicked {count} times</p>
      <button onClick={() => setCount(count + 1)}>
        Click me
      </button>
    </div>
  )
}

In this example, the useEffect hook is called with a function that updates the document title with the current count. The count variable is passed as the second argument, which tells React to only run the effect when the count value changes.

This useEffect hook will run every time the count value changes, updating the document title to reflect the current count. It is a simple example of how you can use the useEffect hook to perform a side effect in a functional component.

You can use the useEffect hook whenever you want to perform a side effect in a functional component. It is a way to use lifecycle methods, such as componentDidMount, componentDidUpdate, and componentWillUnmount, in functional components.

Here are a few examples of when you might want to use the useEffect hook:

When you want to fetch data from an API and update the component state.
When you want to set up a subscription or event listener, and clean it up when the component unmounts.
When you want to perform an action after a component has updated, such as scrolling to an element or focusing on an input.

Overall, the useEffect hook is a very useful and powerful way to add lifecycle methods to functional components in React. It can be used in a wide variety of situations to perform side effects and enable your components to be more interactive and dynamic.

useState vs useEffect

useState and useEffect are both hooks in React that allow you to manage state and side-effects in your component, but they serve different purposes:

useState is used to manage state within a component. It allows you to add state to your component and update it in response to user interactions or other events. It returns a pair of values, the current state and a function to update the state, which you can destructure to separate variables.
useEffect is used to manage side-effects within a component. It allows you to perform actions that affect the component or the outside world in response to changes in the component’s state or props. It takes a callback function as an argument and runs it after the component has rendered.

In short, useState is used to manage the component state, whereas useEffect is used to manage side-effects that happen when component state or props change.

It’s important to note that useState is used to manage the component’s local state and useEffect is used to manage the component’s local state and side-effects, and also the component’s lifecycle.

When to use React useEffect`()` ?

Here are some common use cases where useEffect() can be useful:

Fetching data: When you need to fetch data from an API and update the component’s state in response to the data, you can use useEffect() to fetch the data and update the state when the component is rendered or when specific props or state values change.
Updating the browser’s title: When you want to update the browser’s title based on the current route or some other state, you can use useEffect() to update the title whenever the component is rendered or when specific props or state values change.
Subscribing to an external event: When you need to listen for an event from an external system, such as a websocket, you can use useEffect() to subscribe to the event when the component is rendered and unsubscribe when the component is unmounted.
Setting up and cleaning up an animation: When you need to set up an animation when a component is rendered, such as a carousel, and clean up the animation when the component is unmounted, you can use useEffect() to set up the animation when the component is rendered and clean it up when the component is unmounted.
Adding and removing event listeners: When you need to add and remove event listeners, such as a resize event, you can use useEffect() to add the event listener when the component is rendered and remove it when the component is unmounted.

It’s important to note that useEffect() should be used with caution, as running effects too often or not cleaning them up properly can lead to poor performance and unexpected behavior.

useState vs useEffect

When to use React useEffect() ?

When to use React useEffect`()` ?