一、解决什么问题？
UI 中 JavaScript 错误不应该导致整个应用崩溃，错误边界就是解决方案(React 16 增加的功能)。
二、有哪些特性？
1、定义
- 可捕获子组件 JavaScript 错误，打印错误并展示备用UI的clas组件。
2、无法捕获的错误：
- 事件处理
- 异步代码（例如
setTimeout或requestAnimationFrame回调函数） - 服务端渲染
- 它自身抛出来的错误（并非它的子组件）
3、怎么写？
错误边界是包含下面任意一个或两个方法 的class组件：
static getDerivedStateFromError()：渲染备用 UIcomponentDidCatch()：打印错误信息
// 错误边界 实例
class ErrorBoundary extends React.Component {
constructor(props) {
super(props);
this.state = { hasError: false };
}
static getDerivedStateFromError(error) {
// 更新 state 使下一次渲染能够显示降级后的 UI
return { hasError: true };
}
componentDidCatch(error, errorInfo) {
// 你同样可以将错误日志上报给服务器
logErrorToMyService(error, errorInfo);
}
render() {
if (this.state.hasError) {
// 你可以自定义降级后的 UI 并渲染
return <h1>Something went wrong.</h1>;
}
return this.props.children;
}
}
// 使用 错误边界
<ErrorBoundary>
<MyWidget />
</ErrorBoundary>
4、js代码还是用try / catch 捕获错误
class MyComponent extends React.Component {
constructor(props) {
super(props);
this.state = { error: null };
this.handleClick = this.handleClick.bind(this);
}
handleClick() {
try {
// 执行操作，如有错误则会抛出
} catch (error) {
this.setState({ error });
}
}
render() {
if (this.state.error) {
return <h1>Caught an error.</h1>
}
return <button onClick={this.handleClick}>Click Me</button>
}
}
三、实例展示
一个使用 错误边界 的示例，新建并复制下面代码到index.html文件，浏览器打开index.html即可看到效果。
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8" />
<title>Hello World</title>
<!-- 第一步：加载开发版本的React -->
<script src="https://unpkg.com/react@17/umd/react.development.js"></script>
<script src="https://unpkg.com/react-dom@17/umd/react-dom.development.js"></script>
<!-- 部署时，请用下面链接替代上面 -->
<!-- <script src="https://unpkg.com/react@16/umd/react.production.min.js" crossorigin></script>
<script src="https://unpkg.com/react-dom@16/umd/react-dom.production.min.js" crossorigin></script> -->
<!-- 第二步：加载开发版本的babel -->
<script src="https://unpkg.com/@babel/standalone/babel.min.js"></script>
</head>
<body>
<div id="root"></div>
<script type="text/babel">
class ErrorBoundary extends React.Component {
constructor(props) {
super(props);
this.state = { error: null, errorInfo: null };
}
componentDidCatch(error, errorInfo) {
// Catch errors in any components below and re-render with error message
this.setState({
error: error,
errorInfo: errorInfo
})
// You can also log error messages to an error reporting service here
}
render() {
if (this.state.errorInfo) {
// Error path
return (
<div>
<h2>Something went wrong.</h2>
<details style={{ whiteSpace: 'pre-wrap' }}>
{this.state.error && this.state.error.toString()}
<br />
{this.state.errorInfo.componentStack}
</details>
</div>
);
}
// Normally, just render children
return this.props.children;
}
}
class BuggyCounter extends React.Component {
constructor(props) {
super(props);
this.state = { counter: 0 };
this.handleClick = this.handleClick.bind(this);
}
handleClick() {
this.setState(({ counter }) => ({
counter: counter + 1
}));
}
render() {
if (this.state.counter === 5) {
// Simulate a JS error
throw new Error('I crashed!');
}
return <h1 onClick={this.handleClick}>{this.state.counter}</h1>;
}
}
function Err() {
return (
<div>
<p>
<b>
This is an example of error boundaries in React 16.
<br /><br />
Click on the numbers to increase the counters.
<br />
The counter is programmed to throw when it reaches 5. This simulates a JavaScript error in a component.
</b>
</p>
<hr />
<ErrorBoundary>
<p>These two counters are inside the same error boundary. If one crashes, the error boundary will replace both of them.</p>
<BuggyCounter />
<BuggyCounter />
</ErrorBoundary>
<hr />
<p>These two counters are each inside of their own error boundary. So if one crashes, the other is not affected.</p>
<ErrorBoundary><BuggyCounter /></ErrorBoundary>
<ErrorBoundary><BuggyCounter /></ErrorBoundary>
</div>
);
}
ReactDOM.render(
<Err />,
document.getElementById('root')
);
</script>
</body>
</html>
