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Class Components Life cycle methods React

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M Hassan khan answered on April 2, 2020 Popularity 10/10 Helpfulness 2/10

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Class Components Life cycle methods React

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Class components have lifecycle methods. These for the most part are what useEffect does for function components. They're for doing things like making API calls, starting and ending transitions/animations, debugging, and other things like that. We don't need to use any here, but let's look at a few of the most common ones

constructor isn't necessarily a React lifecylce method but we use it like one. It's where you do things that need to happen before the first render. Generally it's where you set the initial state.
componentDidMount is a function that's called after the first rendering is completed. This pretty similar to a useEffect call that only calls the first time. This is typically where you want to do data fetching. It doesn't have to be async; we just made it async here to make the data fetching easy.
componentDidUpdate is called after your state is updated. If you're doing something like Typeahead where you're making reactive requests to an API based on user input, this would be an ideal place to do it.
componentWillUnmount is typically a place for cleanup. Let's say you had to write a component to integrate with jQuery (I've had to write this, multiple times), this is where you'd clean up those references (like unattaching from DOM nodes and deleting them) so you don't leak memory. This method is invoked whenever a component is about to be destroyed.
This class doesn't cover all the lifecycle methods but you can imagine having different timings for different capabilities of a component can be useful. For example, if you have a set of props that come in and you need to filter those props before you display them, you can use getDerivedStateFromProps. Or if you need to react to your component being removed from the DOM (like if you're subscribing to an API and you need to dispose of the subscription) you can use componentWillUnmount.

There are lots more you can check out in the React docs here.

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Source: Grepper

Tags: class components cycle javascript methods

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Contributed on Jan 12 2023

M Hassan khan

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Functional Component Lifecycle

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Functional Component Lifecycle Diagram for React:

https://wavez.github.io/react-hooks-lifecycle/

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Source: wavez.github.io

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Contributed on Feb 17 2022

KostasX

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lifecycle methods react

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Every component in React goes through a lifecycle of events. I like to think of them as going through a cycle of birth, growth, and death.

Mounting – Birth of your component
Update – Growth of your component
Unmount – Death of your component

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Contributed on Apr 02 2020

Ankur

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react lifecycle

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Initialization = setup props & state

// Lifecycle Phase 
1. mounting // Born
2. update   // Growth
3. unmounting //Dead

// lifecycle method
mounting = constructor->render->componentDidMount
update = render->componentDidUpdate
unmounting = componentWillUnmount

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Contributed on Aug 20 2022

azonedev

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reactjs lifecycle class components

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import React from 'react';
import ReactDOM from 'react-dom';
 
class Test extends React.Component {
    constructor(props)
    {
        super(props);
        this.state = { hello : "World!" };
    }
 
    componentWillMount()
    {
        console.log("componentWillMount()");
    }
 
    componentDidMount()
    {
        console.log("componentDidMount()");
    }
 
    changeState()
    {
        this.setState({ hello : "Geek!" });
    }
 
    render()
    {
        return (
            <div>
            <h1>GeeksForGeeks.org, Hello{ this.state.hello }</h1>
            <h2>
            <a onClick={this.changeState.bind(this)}>Press Here!</a>
            </h2>
            </div>);
    }
 
    shouldComponentUpdate(nextProps, nextState)
    {
        console.log("shouldComponentUpdate()");
        return true;
    }
 
    componentWillUpdate()
    {
        console.log("componentWillUpdate()");
    }
 
    componentDidUpdate()
    {
        console.log("componentDidUpdate()");
    }
}
 
ReactDOM.render(
    <Test />,
    document.getElementById('root'));

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Source: www.geeksforgeeks.org

Tags: class clas

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Contributed on Dec 24 2021

Rizz

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React Component Lifecycle

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What is the order that Class components run when React initialize and mounts 
the components.

1. Regardless of React Components, constructors are always ran first 
	1. In constructor, you will just initialize the state in constructor
2. Render runs second, which determines what to show. This is the template 
   of the HTML and dictates the UI is going to be.
3. Third one that runs is componentDidMount, React runs the constructor, 
   runs the render and mounts the initial state and mounts on. Then it 
   will runs the code in componentDidMount();
   
- When setState() is called, the render() method will be called again and 
  re-renders.
	- Every subsequent child with a different props will also be re-rendered.

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Contributed on Jul 23 2022

Average Armadillo

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React Component Lifecycle Mounting

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-1

import React, { Component } from 'react';

class Counter extends Component {
  constructor(props) {
    super(props);
    this.state = {
      count: 0
    };
    this.handleClick = this.handleClick.bind(this);
  }

  handleClick() {
    this.setState(prevState => ({
      count: prevState.count + 1
    }));
  }

  render() {
    return (
      <div>
        <p>Count: {this.state.count}</p>
        <button onClick={this.handleClick}>Increment</button>
      </div>
    );
  }
}

export default Counter;

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Source: www.freecodecamp.org

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Contributed on Dec 13 2023

Özkan Kaya

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Class Components Life cycle methods React

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