每次单击increment按钮时:
期望:当前count已记录
实际:count的初始值,即记录为3
import React, { useState, useEffect } from "react";
function SomeLibrary(props) {
const [mapState, setMapState] = useState(undefined);
useEffect(() => {
console.log("setting map");
// Run exactly once at mount of com
下面是我的代码:
function State(){
var [msg,set_msg]=React.useState("hello") //not rendered, just to force render
var [data,set_data]=React.useState({version:1})
function onClick(){
set_msg(x=>x+'x') //just to force render
data.version+=1 //changing state in place, but it still
你好,我正在尝试将exportTest导出到另一个js文件,然后重新渲染。我正试着这样做
import React, { useState } from 'react';
import { StyleSheet, View } from 'react-native';
var n;
export var exportTest;
function foo()
{
//doing something and giving back n as 1 or 0
}
export default function App () {
const [test,s
只是想知道这里出了什么问题(我是新来的反应)。当用户在input中进行查询时,我的fetch请求可以工作,并从后端输入数据。但现在我收到了这个错误。
RecipeDBTest.jsx:54 Uncaught TypeError: Cannot read properties of undefined (reading 'recipe_name')
at GetRecipe (RecipeDBTest.jsx:54:1)
at renderWithHooks (react-dom.development.js:16175:1)
at mountIndete
在使用react构建的应用程序中,我有一个简单的函数,它在onClick event上添加了一个表单文本字段。当用户单击"add按钮“时,我使用map()添加更多字段。当我需要表单文本字段时,当用户单击map()时只返回一次,add employees button就会重新调整它两次。如何编辑代码以只返回文本字段?
import { React, useState } from "react";
import { Button, Form } from "react-bootstrap";
import { Col } from "react-