Reactjs 如何指定带有功能组件的构造函数(粗箭头语法)

发布于05月30日

鉴于这一组成部分:

import React from 'react'
import ReactDOM from 'react-dom'
import PropTypes from 'prop-types'

const NewGoalInput = props => {
  return (
    <input type="text" onKeyUp={handleKeyUp}/>
  )
}

const handleKeyUp = (e) => {
  if (e.key === "Enter") {
    // TODO Add goal
  }
}

export default NewGoalInput

我如何添加一个构造函数，在其中我可以定义状态，而不必使用extends React.Component语法？

推荐答案

因为它是一个无状态组件，所以没有组件生命周期.

你必须扩展React.Component来创建一个有状态的组件，然后需要一个构造函数，你就可以使用state了.

Update

Hooks are a new feature proposal that lets you use state and other React > features without writing a class. They are released in React as a part of > v16.8.0

Stateless:

import React from "react"

const Stateless = ({name}) => (
  <div>{`Hi ${name}`}</div>
);

Stateful:

可以访问组件生命周期方法和本地状态.

class Stateful extends React.Component {
  constructor(props) {
    super(props);
    this.state = {
      count: 0
    };
  }

  componentDidMount() {
    const { count } = this.state;
    document.title = `You've clicked ${count} times.`;
  }

  componentDidUpdate() {
    const { count } = this.state;
    document.title = `You've clicked ${count} times.`;
  }

  render() {
    const { count } = this.state;
    return (
      <div>
        <p>You've clicked {count} times.</p>
        <button onClick={() => this.setState({ count: count + 1 })}>
          Click me
        </button>
      </div>
    );
  }
}

Using Hooks:

能够使用State Hook和Effect Hook.

如果您熟悉React类生命周期方法，可以将useEffect钩子视为componentDidMount、componentDidUpdate和componentWillUnmount的组合.

import React, { useState, useEffect } from "react";

const UsingHooks = () => {
  const [count, setCount] = useState(0);

  // Similar to componentDidMount and componentDidUpdate:
  useEffect(() => {
    // Update the document title using the browser API
    document.title = `You've clicked ${count} times.`;
  });

  return (
    // <> is a short syntax for <React.Fragment> and can be used instead of a wrapping div
    <>
      <p>You've clicked {count} times.</p>
      <button onClick={() => setCount(count + 1)}>
        Click me
      </button>
    </>
  );
}