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react useEffect life cycle

Clever Cowfish answered on April 14, 2022 Popularity 10/10 Helpfulness 3/10

answer react useEffect life cycle

related react functional lifecycle methods with useEffect hook

react useEffect life cycle

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useEffect( () => console.log("mount"), [] );
useEffect( () => console.log("data1 update"), [ data1 ] );
useEffect( () => console.log("any update") );
useEffect( () => () => console.log("data1 update or unmount"), [ data1 ] );
useEffect( () => () => console.log("unmount"), [] );

Popularity 10/10 Helpfulness 3/10 Language javascript

Source: stackoverflow.com

Tags: cycle javascript use-effect

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Contributed on Apr 14 2022

Clever Cowfish

0 Answers Avg Quality 2/10

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react functional lifecycle methods with useEffect hook

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# React Component Lifecycles and useEffect Hook

React component lifecycle can be divided into three main phases: mounting, updating, and unmounting. These phases provide us with lifecycle methods or hooks to manage and control what happens at each stage. In this tutorial, we will explore these lifecycle phases and how to handle them using the `useEffect` hook in functional components.

## Table of Contents

1. Component Lifecycles Overview
2. useEffect Hook
3. Examples
    - Using useEffect for Mounting
    - Using useEffect for Updating
    - Using useEffect for Conditional Updating
    - Using useEffect for Unmounting

<hr/>

## 1. Component Lifecycles Overview

When a component is created and inserted into the DOM, it undergoes the **Mounting** phase. This is the ideal phase to perform setup operations like fetching data, setting up subscriptions, or initializing state.

When a component's state or props change, it enters the **Updating** phase. This phase is useful to react to changes in props or state, perform calculations, or trigger re-renders.

When a component is removed from the DOM, it undergoes the **Unmounting** phase. This is the ideal phase to perform cleanup tasks like invalidating timers, canceling network requests, or cleaning up any subscriptions that were created in componentDidMount().

<hr/>

## 2. useEffect Hook

In functional components, the `useEffect` hook allows us to perform side effects. It takes two arguments: a function that contains the side-effect logic and a dependencies array. 

```javascript
useEffect(() => {
  // side-effect logic here
}, [/* dependencies array */]);
```

<hr/>

## 3. Examples

### 3.1 Using useEffect for Mounting

If you want to run an effect function only once, when the component mounts, you can pass an empty array (`[]`) as the second argument. 

```javascript
useEffect(() => {
  console.log('Component mounted');
}, []);
```

### 3.2 Using useEffect for Updating

To run an effect function on every render (mounting and updating), you can pass no second argument. 

```javascript
useEffect(() => {
  console.log('Component mounted or updated');
});
```

### 3.3 Using useEffect for Conditional Updating

If you want to run an effect function only when certain values have changed, you can pass those values in the dependencies array. 

```javascript
const [count, setCount] = useState(0);

useEffect(() => {
  console.log('Count value changed');
}, [count]);
```

### 3.4 Using useEffect for Unmounting

To perform cleanup on unmount, you can return a function from your effect function. 

```javascript
useEffect(() => {
  console.log('Component mounted');

  return () => {
    console.log('Component unmounted');
  };
}, []);
```

<hr/>

Popularity 9/10 Helpfulness 2/10 Language whatever

Source: chat.openai.com

Tags: hook lifecycle

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Contributed on Jun 17 2023

Dead Dugong

0 Answers Avg Quality 2/10

react useEffect life cycle

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