ReactJS fetch 导致无限循环

Posted 2023-03-27

【中文标题】ReactJS fetch 导致无限循环

【英文标题】：ReactJS fetch causes infinite loop

【发布时间】：2019-04-07 17:29:06

【问题描述】：

我有两个应用，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 fetch 方法时，它会创建无限循环。如何解决？

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。

【问题讨论】：

你在哪里调用drawTable()函数？

@Jayce444 我在渲染中调用函数，返回方法如下：this.drawTable(this.props)

您在 render 方法中调用 drawTable，这会导致一个 fetch 请求。完成后，您将响应置于setState 状态，这会导致您的组件重新渲染，并且它会无限期地继续下去。您可以改为获取 componentDidMount 和 componentDidUpdate 中的数据。

@Tholle 非常感谢您的回答！我完全明白了，但我仍然无法在我的代码中实现它。如何在代码中实现它？

阅读reactjs.org/docs/react-component.html#render

【参考方案1】：

您在渲染方法中调用drawTable，这会导致获取请求。完成后，您将响应置于setState 状态，这会导致您的组件重新渲染，并且它会无限期地继续下去。

您可以改为获取 componentDidMount 和 componentDidUpdate 中的数据，然后在 render 方法中使用数据。

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() 
    // ...