如何防止 React 重新渲染整个组件

Question

I have a prop called isMobile that displays an external iframe. When I tilt the screen on an iPad, this will change the prop to change values and re-render the iframe (losing all progress inside the iframe).

What is a good way of preventing that re-render? The docs say that I shouldn't use shouldComponentUpdate , since that only is a performance optimization.

Answer 1

As some answers said, you can use a React.PureComponent that it avoid to re-render with any reason to do it, so you can fix it, separating your Iframe into a single component with the React.PureComponent so it would be like this:

class MyPureIframe extends React.PureComponent {
  render() {
    const {src, width, height} = this.props;
    return (
      <iframe src={src} width={width} height={height} {...whateverProps} />
    );
  }
}

class MyNormalView extends React.Component {
  render() {
    return (
      <div>
       <!--SOME MARKUP HERE-->
       <MyPureIframe src={'https://your-url-to-iframe'} width={100} height={100} />
       <!--SOME MARKUP HERE-->
      </div>
    );
  }
}

So the MyPureIframe only will change (re-render) when some of its props change (src, width, height, or other that you passed down).

In that way no matters in the MyNormalView re-render the deep component MyPureIframe won't re-render until any of its props changed.

I hope it can help you.

Updated May 2020

Because the answer above is related for class based component, if you use a functional component, it mean a function that render some html markup, you can still use this approach as follow.

import React, {memo} from 'react';

const MyPureIframe = memo(({src, width, height}) => (
  <iframe src={src} width={width} height={height} {...whateverProps}/>
));

class MyNormalView extends React.Component {
  render() {
    return (
      <div>
       <!--SOME MARKUP HERE-->
       <MyPureIframe src={'https://your-url-to-iframe'} width={100} height={100} />
       <!--SOME MARKUP HERE-->
      </div>
    );
  }
}

Doing like so, you will get the same result, but using a functional component instead.

Hope it helps you.

Answer 2

shouldComponentUpdate is not a better approach. The document says it can ignore the changes to shouldComponentUpdate in future. Please try using the concept called memoize which is better than PureComponent