Question

ReactJS fetch 导致无限循环

2018-11-03

9569

javascript reactjs

我有两个应用程序，其中一个是 NodeJS，监听 5000 的端口，另一个是 ReactJS，监听 3000 的端口。

我可以像这样从 NodeJS 返回 JSON（ http://localhost:5000/api/28/10/2018 ）：

{
  "date": "28.10.2018",
  "across": [
    {"no": "1", "text": "Warning about an incoming projectile"},
    {"no": "5", "text": "Rapper/producer behind Beats headphones"},
    {"no": "6", "text": "Noble gas below xenon on the periodic table"},
    {"no": "7", "text": "Setting for much of \"Finding Nemo\""},
    {"no": "8", "text": "Looney Tunes character who says \"Th-th-th-that's all, folks!\""}
  ],
  "down": [
    {"no": "1", "text": "Harry's enemy at Hogwarts"},
    {"no": "2", "text": "Milk dispenser"},
    {"no": "3", "text": "Sound from a frog"},
    {"no": "4", "text": "Country music star Chesney"},
    {"no": "5", "text": "The shape of water?"}
  ],
  "cells": ["-1","1","2","3","4","5","0","0","0","0","6","0","0","0","0","7","0","0","0","0","8","0","0","0","0"]
}

我想用 ReactJS 显示这些数据，但是当我尝试获取方法时，它会创建无限循环。如何解决这个问题？

我的 ReactJS 代码：

drawTable = (props) => {
  /* Some if-elseif that is not related to the question */
  else {
    // here props.type get an array that hold input from terminal
    let day, month, year;
    day = props.type[1];
    month = props.type[2];
    year = props.type[3];

    if (day === undefined || month === undefined || year === undefined) {
      console.log("Please use get-old command properly!");
      console.log("Usage:\nget-old day month year");
      console.log("Example:\nget-old 28 10 2018");
      return idle;
    }
    // If arguments defined go fetch
    let url = `http://localhost:${REACT_PORT}/old/${day}/${month}/${year}`;
    fetch(url)
    .then((response) => response.json())
    .then((data) => {
      this.setState({data: data});
    })
    .catch((error) => {
      console.error(error);
    });
    console.log(this.state.data);
  }
}

这记录了许多 JSON 对象。

Answer 1

在 render 方法中调用 drawTable ，这将引发获取请求。完成后，使用 setState 将响应置于状态，这将导致组件重新渲染，并无限期地继续下去。

您可以改为在 componentDidMount 和 componentDidUpdate 中获取数据，然后只在 render 方法中使用这些数据。

示例

class MyComponent extends React.Component {
  // ...

  componentDidMount() {
    this.fetchData();
  }

  componentDidUpdate(prevProps) {
    const [, prevDay, prevMonth, prevYear] = prevProps.type;
    const [, day, month, year] = this.props.type;

    if (prevDay !== day || prevMonth !== month || prevYear !== year) {
      this.fetchData();
    }
  }

  fetchData = () => {
    const [, day, month, year] = this.props.type;
    const url = `http://localhost:${REACT_PORT}/old/${day}/${month}/${year}`;

    fetch(url)
      .then(response => response.json())
      .then(data => {
        this.setState({ data });
      })
      .catch(error => {
        console.error(error);
      });
  };

  render() {
    // ...
  }
}