How React distinguishes components defined by Class and function

React distinguishes components defined by Class and function: 1. Use function to define components, and add hooks to allow components defined by function to have local state; 2. Use class to define components, and filter out the second parameter of qs prefix.

The operating environment of this tutorial: Windows 7 system, React version 16.8. This method is suitable for all brands of computers.

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React distinguishes the component methods defined by Class and function:

Use function to define components

import React, { useState, useEffect } from "react";
import { useLocation } from "react-router-dom";
import qs from "qs"; //qs用来格式化数据
import { movieDetail } from "../../services/movies";

//推荐使用function定义组件,react16.8以后新增hook可以让function定义的组件具有局部state

export default function Detail() {
  //function定义的组件没有局部的数据，所以使用useState()获取局部数据（局部状态）
  //以下例子第一个参数表示定义的数据，第二个参数表示更改此数据要用到的方法，useState()中的参数表示定义数据的初始值
  //也就是movie={video:{}} 若要定义多个值，多次使用useState就行了
  const [movie, setMovie] = useState({
    video: {},
  });
  const [live, sertLive] = useState({}); //live={}
  //function定义的组件不能使用this.props.location来获取地址栏信息，使用useLocation()获取地址栏信息
  const location = useLocation();
  console.log(location);

  //function定义的组件也没有生命周期的钩子函数，我们使用useEffect来模拟生命周期,
  //参数一表示参数二依赖的内容发生改变之后触发的回调函数，如果参数二为空数组表示只执行一次（初始化执行）
  useEffect(() => {
    const query = qs.parse(location.search, {
      ignoreQueryPrefix: true, //此参数表示过滤掉前缀
    });
    //useEffect中调用异步函数如下所示
    async function fetchData() {
      // You can await here
      const result = await movieDetail(query.id);
      console.log(result);
      setMovie(result.data.data.basic);
      sertLive(result.data.data.live);
    }
    fetchData();
  }, []);
  return (
    <div>
      <img
        style={{ width: "100%", margin: "0 auto", display: "block" }}
        src={live.img}
      ></img>
      <h1>{movie.name}</h1>
      <p>{movie.story}</p>
      <video controls autoPlay src={movie.video.url}></video>
    </div>
  );
}

Use class to define components

import React, { useState, useEffect, Component} from "react";
import { useLocation } from "react-router-dom";
import qs from "qs"; //qs用来格式化数据
import { movieDetail } from "../../services/movies";

//使用class定义组件中this指向复杂，不推荐使用

export default class Detail extends Component {
  constructor(props) {
    super(props);
    console.log(props);
    this.state = {
      movie: {
        video: {
          url: "",
        },
      },
    };
  }
  async componentDidMount() {
    console.log(this.props.location.search); //url传参
    //qs第二个参数表示过滤掉前缀
    const query = qs.parse(this.props.location.search, {
      ignoreQueryPrefix: true,
    });
    console.log(query);
    const result = await movieDetail(query.id);
    console.log(result);
    this.setState({
      movie: result.data.data.basic,
    });
    document
      .querySelectorAll(".nav ul li")[1]
      .querySelector("a")
      .classList.add("active");
  }
  componentWillUnmount() {
    document
      .querySelectorAll(".nav ul li")[1]
      .querySelector("a")
      .classList.remove("active");
  }
  render() {
    return (
      <div>
        <h1>{this.state.movie.name}</h1>
        <p>{this.state.movie.story}</p>
        <video controls autoPlay src={this.state.movie.video.url}></video>
      </div>
    );
  }
}

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