How to use shouldComponentUpdate with React Hooks?

问题

I've been reading these links:
https://reactjs.org/docs/hooks-faq.html#how-do-i-implement-shouldcomponentupdate
https://reactjs.org/blog/2018/10/23/react-v-16-6.html

In the first link it says (https://reactjs.org/docs/hooks-faq.html#from-classes-to-hooks):

shouldComponentUpdate: See React.memo

The second link also states that:

Class components can bail out from rendering when their input props are the same using PureComponent or shouldComponentUpdate. Now you can do the same with function components by wrapping them in React.memo.

What is desired:

I want Modal to render only when the Modal is visible (managed by this.props.show)

For class component:

shouldComponentUpdate(nextProps, nextState) {
    return nextProps.show !== this.props.show;
}

How can I use memo instead in a functional component - here, in Modal.jsx?

The related code:

Functional component Modal.jsx (I don't know how to check for props.show)



import React, { useEffect } from 'react';
import styles from './Modal.module.css';
import BackDrop from '../BackDrop/BackDrop';

const Modal = React.memo(props => {
  useEffect(() => console.log('it did update'));

  return (
    <React.Fragment>
      <BackDrop show={props.show} clicked={props.modalClosed} />
      <div
        className={styles.Modal}
        style={{
          transform: props.show ? 'translateY(0)' : 'translateY(-100vh)',
          opacity: props.show ? '1' : '0'
        }}>
        {props.children}
      </div>
    </React.Fragment>
  );
});

export default Modal;

The part of class component PizzaMaker jsx that renders Modal:



 return (
      <React.Fragment>
        <Modal show={this.state.purchasing} modalClosed={this.purchaseCancel}>
          <OrderSummary
            ingredients={this.state.ingredients}
            purchaseCancelled={this.purchaseCancel}
            purchaseContinued={this.purchaseContinue}
            price={this.state.totalPrice}
          />
        </Modal>
        ...
      </React.Fragment>
    );

回答1:

Here is the documentation for React.memo

You can pass a function to control the comparison :

const Modal = React.memo(
  props => {...},
  (prevProps, nextProps) => prevProps.show === nextProps.show
);

when the function returns true, the component will not be re-rendered

来源：https://stackoverflow.com/questions/56297351/how-to-use-shouldcomponentupdate-with-react-hooks

标签

javascript

reactjs

functional-programming

react-hooks