React.js Tutorial: React Component Lifecycle
Introduction about React component lifecycle.
1 Lifecycle
A React component in browser can be any of the following three statuses: mounted, update and unmounted.
So React component lifecycle can be divided into three phases according to these statuses: mounting, updating and unmounting.
2 Mounting
React.js exposed interfaces or hook methods in each phase of component lifecycle.
2.1 Initializing state
You can optionally set initial state value in constructor()
method of the component if you are using ES6
syntax.
const tom_and_jerry = [
{
name: 'Tom',
score: 55
},
{
name: 'Jerry',
score: 80
}
];
class ScoreBoard extends React.Component {
constructor(props) {
super(props);
this.state = { players: tom_and_jerry }
}
// ...
}
If you are using ES5
syntax, getInitialState()
in the right place to initialize component state.
var ScoreBoard = React.createClass({
getInitialState: function() {
return {
players: tom_and_jerry
}
},
// ...
});
The getInitialState()
method is called only one time before the component is mounted.
Initialization of state should typically only be done in a top level component, which acts as a role of controller view in your page.
2.2 Default props
You can also define default values of component props (properties) if the parent component does not declare their values.
Return default props using ES7+
static property initializer.
class SinglePlayer extends React.Component {
static defaultProps = {
name: 'Nobody',
score: 0
}
// ...
}
Default props in ES6
:
class SinglePlayer extends React.Component {
// ...
}
SinglePlayer.defaultProps = {
name: 'Nobody',
score: 0
}
You can define getDefaultProps()
method in ES5
.
var SinglePlayer = React.createClass({
getDefaultProps: function() {
return {
name: 'Nobody',
score: 0
}
}
});
The getDefaultProps()
method is called only once before any instance of the component is created. So you should avoid using this.props
inside getDefaultProps()
method.
2.3 componentWillMount()
The componentWillMount()
method is invoked only once before initial rendering.
It is also a good place to set initial state value inside componentWillMount()
.
class SinglePlayer extends React.Component {
componentWillMount() {
this.setState({
isPassed: this.props.score >= 60
});
alert('componentWillMount => ' + this.props.name);
console.log('componentWillMount => ' + this.props.name);
}
// ...
}
2.4 componentDidMount()
This lifecycle method will be invoked after rendering.
It is the right place to access DOM of the component.
class ScoreBoard extends React.Component {
constructor(props) {
super(props);
this._handleScroll = this.handleScroll.bind(this);
}
handleScroll() {}
componentDidMount() {
alert('componentDidMount in NoticeBoard');
window.addEventListener('scroll', this._handleScroll);
}
// ...
}
3 Updating
3.1 componentWillReceiveProps()
void componentWillReceiveProps(object nextProps)
This method will be invoked when a component is receiving new props. componentWillReceiveProps()
won't be called for the initial rendering.
class SinglePlayer extends React.Component {
componentWillReceiveProps(nextProps) {
// Calculate state according to props changes
this.setState({
isPassed: nextProps.score >= 60
});
}
}
The old props can be accessed via this.props
inside componentWillReceiveProps()
. Typically, you can set state according to changes of props in this method.
3.2 shouldComponentUpdate()
boolean shouldComponentUpdate(object nextProps,
object nextState)
shouldComponentUpdate()
will be invoked before rendering when new props or state are being received. This method won't be called on initial rendering.
shouldComponentUpdate()
returns true
by default.
This method is usually an opportunity to prevent the unnecessary rerendering considering performance. Just let shouldComponentUpdate()
return false
, then the render()
method of the component will be completely skipped until the next props or state change.
class SinglePlayer extends React.Component {
shouldComponentUpdate(nextProps, nextState) {
// Don't rerender if score doesn't change,
if ( nextProps.score == this.props.score ) {
return false;
}
return true;
}
}
3.3 componentWillUpdate()
void componentWillUpdate(object nextProps,
object nextState)
Invoked just before render()
, but after shouldComponentUpdate()
(of course, return a true
). This method is not called for the initial rendering.
Use this as an opportunity to prepare for an update.
class SinglePlayer extends React.Component {
componentWillUpdate(nextProps, nextState) {
alert('componentWillUpdate => ' + this.props.name);
console.log('componentWillUpdate => ' + this.props.name);
}
}
3.4 componentDidUpdate()
void componentDidUpdate(object prevProps,
object prevState)
Invoked immediately after the component's updates are flushed to the DOM. This method is not called for the initial rendering.
You can perform DOM operations after an update inside this function.
class SinglePlayer extends React.Component {
componentDidUpdate(prevProps, prevState) {
alert('componentDidUpdate => ' + this.props.name);
console.log('componentDidUpdate => ' + this.props.name);
}
}
4 Unmounting
void componentWillUnmount()
This is invoked immediately before a component is unmounted or removed from the DOM.
Use this as an opportunity to perform cleanup operations. For example, unbind event listeners here to avoid memory leaking.
class ScoreBoard extends React.Component {
componentWillUnmount() {
window.removeEventListener('scroll', this._handleScroll);
}
}
5 Sample codes
Complete sample codes to log each lifecycle method call in browser's console.
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>React Component Lifecycle Demo</title>
<!-- react includes two parts: react.js and react-dom.js -->
<script src="//fb.me/react-15.2.1.js"></script>
<script src="//fb.me/react-dom-15.2.1.js"></script>
<!-- babel standalone -->
<script src="//cdnjs.cloudflare.com/ajax/libs/babel-standalone/6.10.3/babel.min.js"></script>
</head>
<body>
<div id="app"></div>
<script type="text/babel">
const tom_and_jerry = [
{
name: 'Tom',
score: 55
},
{
name: 'Jerry',
score: 80
}
];
class SinglePlayer extends React.Component {
constructor(props) {
super(props);
this.state = { isPassed: false }
}
componentWillMount() {
// Mark it as 'Pass' if score >= 60
this.setState({
isPassed: this.props.score >= 60
});
console.log('componentWillMount => ' + this.props.name);
alert('componentWillMount => ' + this.props.name);
}
componentDidMount() {
console.log('componentDidMount => ' + this.props.name);
alert('componentDidMount => ' + this.props.name);
}
componentWillReceiveProps(nextProps) {
// Calculate state according to props changes
this.setState({
isPassed: nextProps.score >= 60
});
console.log('componentWillReceiveProps => ' + this.props.name + ': ' + nextProps.score);
alert('componentWillReceiveProps => ' + this.props.name + ': ' + nextProps.score);
}
shouldComponentUpdate(nextProps, nextState) {
// Don't rerender if score doesn't change,
if ( nextProps.score == this.props.score ) {
console.log('shouldComponentUpdate => ' + this.props.name + '? false');
alert('shouldComponentUpdate => ' + this.props.name + '? false');
return false;
}
console.log('shouldComponentUpdate => ' + this.props.name + '? true');
alert('shouldComponentUpdate => ' + this.props.name + '? true');
return true;
}
componentWillUpdate(nextProps, nextState) {
console.log('componentWillUpdate => ' + this.props.name);
alert('componentWillUpdate => ' + this.props.name);
}
componentDidUpdate(prevProps, prevState) {
console.log('componentDidUpdate => ' + this.props.name);
alert('componentDidUpdate => ' + this.props.name);
}
componentWillUnmount() {
console.log('componentDidUpdate => ' + this.props.name);
alert('componentDidUpdate => ' + this.props.name);
}
render() {
console.log("render => " + this.props.name);
return (
<div>
<h5><span>Name: </span>{this.props.name}</h5>
<p><span>Score: </span><em>{this.props.score}</em></p>
<p><span>Pass: </span><input type="checkbox" defaultChecked={this.state.isPassed} disabled={true} /></p>
</div>
);
}
}
class ScoreBoard extends React.Component {
constructor(props) {
super(props);
this.state = {
players: tom_and_jerry
};
}
changeScore(amount) {
if ( typeof(amount) != "number" ) {
return;
}
let players = this.state.players;
let tom = players[0];
tom.score = tom.score + amount;
tom.score = (tom.score > 100) ? 100 : tom.score;
tom.score = (tom.score < 0) ? 0 : tom.score;
players[0] = tom;
this.setState({ players: players });
}
render() {
return (
<div>
<h4>Score Board</h4>
<div>
<button onClick={ (amount) => this.changeScore(5) }>Score of Tom: +5</button>
<button onClick={ (amount) => this.changeScore(-5) }>Score of Tom: -5</button>
</div>
{
this.state.players.map((v, idx) => {
return <SinglePlayer key={idx} name={v.name} score={v.score} />
})
}
</div>
);
}
}
class App extends React.Component {
render() {
return (
<div>
<h1>React Component Lifecycle Demo</h1>
<ScoreBoard />
</div>
)
}
}
// Mount root App component
ReactDOM.render(<App />, document.getElementById('app'));
</script>
</body>
</html>
https://www.codevoila.com/post/57/reactjs-tutorial-react-component-lifecycle
React.js Tutorial: React Component Lifecycle的更多相关文章
- WHAT IS THE DIFFERENCE BETWEEN REACT.JS AND REACT NATIVE?
Amit Ashwini - 09 SEPTEMBER 2017 React.js was developed by Facebook to address its need for a dynami ...
- [React] 10 - Tutorial: router
Ref: REACT JS TUTORIAL #6 - React Router & Intro to Single Page Apps with React JS Ref: REACT JS ...
- React.js入门笔记
# React.js入门笔记 核心提示 这是本人学习react.js的第一篇入门笔记,估计也会是该系列涵盖内容最多的笔记,主要内容来自英文官方文档的快速上手部分和阮一峰博客教程.当然,还有我自己尝试的 ...
- Facebook React.js库 入门实例教程
作者: 阮一峰 日期: 2015年3月31日 现在最热门的前端框架,毫无疑问是 React . 上周,基于 React 的 React Native 发布,结果一天之内,就获得了 5000 颗星,受瞩 ...
- React.js入门
React 入门实例教程 现在最热门的前端框架,毫无疑问是 React . 上周,基于 React 的 React Native 发布,结果一天之内,就获得了 5000 颗星,受瞩目程度可见一斑. ...
- 13个精选的React JS框架
如果你正在使用 React.js 或 React Native 创建用户界面,可以试一试本文推荐的这些框架. React.js 和 React Native 是流行的用户界面(UI)开发平台,且都是开 ...
- React JS 基础知识17条
1. 基础实例 <!DOCTYPE html> <html> <head> <script src="../build/react.js" ...
- react.js 从零开始(一)
React 是什么? 网络上的解释很多...我这里把他定义为 通过javascript 的形式组件化 html的框架... React 仅仅是 VIEW 层. React 提供了模板语法以及一些函数钩 ...
- 【每天半小时学框架】——React.js的模板语法与组件概念
[重点提前说:组件化与虚拟DOM是React.js的核心理念!] 先抛出一个论题:在React.js中,JSX语法提倡将 HTML 和 CSS 全都写入到JavaScrip ...
随机推荐
- DestroyImmediate和Destroy
DestroyImmediate立即对对像进行销毁并从内存中移除: Destroy销毁场景中的物体,但内存中还存在,当令它需要销毁时,只是给一个标识.而内存中它依然是存在的,只有当内存不够,或一段时间 ...
- 排行榜 和 zset
ZSET 使用 https://blog.csdn.net/weixin_37490221/article/details/78135036 https://www.cnblogs.com/chenz ...
- lower_bound()和upper_bound()
lower_bound()和upper_bound() 是方便的在有序数组中二分查找的函数,并且在STL其他数据结构中也提供该方法(如map和set). 但是两函数并不是二分查找"小于&qu ...
- STL源码剖析——序列式容器#5 heap
准确来讲,heap并不属于STL容器,但它是其中一个容器priority queue必不可少的一部分.顾名思义,priority queue就是优先级队列,允许用户以任何次序将任何元素加入容器内,但取 ...
- Google大数据三篇著名论文中文版
Google File System中文版 Google MapReduce中文版 Google Bigtable中文版
- FusionInsight大数据开发---Oozie应用开发
Oozie应用开发 要求: 了解Oozie应用开发适用场景 掌握Oozie应用开发 熟悉并使用Oozie常用API Oozie简介 Oozie是一个Hadoop作业的工作流调度管理系统 Oozie工作 ...
- CodeForces 1228F One Node is Gone
洛谷题目页面传送门 & CodeForces题目页面传送门 给定一棵树\(T=(V,E),|V|=2^n-2,|E|=2^n-3\),输出所有的\(x\),使得存在一棵满二叉树\(T'\),将 ...
- Java自学-操作符 算数操作符
Java的算数操作符 算数操作符 基本的有: + - * / % 自增 自减 ++ -- 基本的加 减 乘 除: public class HelloWorld { public static voi ...
- 2.JavaScript中的原型规则以及原型设计模式
原型规则 原型规则 所有的引用类型(数组.对象.函数),都具有对象特征,即可自由扩展属性: 所有的引用类型,都有一个_proto_ 属性(隐式原型),属性值是一个普通对象: 所有函数,都具有一个pro ...
- PHPSocket.IO知识学习整理
一.服务端和客户端连接 1.创建一个SocketIO服务端 <?php require_once __DIR__ . '/vendor/autoload.php'; use Workerman\ ...