reactjs

问题 const { useState } = React; const App = () => { const [num, setNum] = useState(0); return ( <input type="number" value={num} onChange={(e)=>setNum(parseInt(e.target.value))} /> ) } ReactDOM.render(<App />, document.getElementById('root')); <script crossorigin src="https://unpkg.com/react@16/umd/react.development.js"></script> <script crossorigin src="https://unpkg.com/react-dom@16/umd/react-dom.development.js"></script> <div id="root" /> I want to keep num 's type as Number , not String . but

问题 Hey guys am trying to run a webrtc video call using react, node, socket and peerjs, if i try starting a video chat with chrome it works, if i run chrome as private and connect as second user using the video link it works but if i try connecting from another browser using same video link e.g edge or opera it doesn't work instead it console log an error.. My code import React from 'react' import io from 'socket.io-client' import Peer from 'peerjs' import './ClassWall.css' const socket = io

问题 I am trying to send a new membership from a form in react to my express server to add to the mailchimp memberlist I am getting a cors error and I don't know if I am missing any proxys. I want a user to be able to sign up in react and then it sends it to the mailchimp database I have been able to get the members list but I am not allowed to post to it : This is my express backend : const express = require('express'); const Mailchimp = require('mailchimp-api-v3'); require('dotenv').config();

问题 I recently started using Gatsby for building my websites, previously I relied just on plain html and css, so I may be missing something really basic here... I am trying to style a custom header component that looks like this import React from "react" import MWidth from "./m-width" import logo from "../resources/images/logo.png" function Header() { return ( <> <MWidth> <div> <img src={`${logo}`}></img> </div> </MWidth> </> ) } export default Header after importing it inside the layout

问题 I'm just starting to use react hooks and I'm having some issues when using custom hooks. It's probably lack of understanding but here's what I'm attempting My Custom hook: import React, { useState } from "react" export const useValidateContent = initState => { const[valid, setValid] = useState(initState) const[errorMsg, setErrorMsg] = useState(null) const validate = () => { // Update component state to test setValid(false) setErrorMsg('Some error found') } return [valid, validate, errorMsg] }

问题 I tried to track the number of times react component is rendered. However, it seems that the renderCounter gets incremented by 2 each time. Why does this happen? I know it is a bad practice to use global variables, but I'm interested in the reason why this happens. https://codesandbox.io/s/rendercounter-does-not-increment-correctly-093ok?file=/src/App.js let renderCounter = 1; function App() { const [i, inc] = useReducer((_) => _ + 1, 1); // render console.log(JSON.stringify(i), "th click");

问题 I am getting a "Cannot read property 'style' of null" on my getElementById('password'), but its clearly defined on the page. I'm new to react, and I'm guessing this isn't allowed or something. But I'm trying to have the password page show until, its style is changed to "none", which happens in a different component. function App() { const [loggedIn, setLoggedIn] = useState(false) if (document.getElementById('password').style.display = "block"){ setLoggedIn(false) } else { setLoggedIn(true) }

问题 I am getting a "Cannot read property 'style' of null" on my getElementById('password'), but its clearly defined on the page. I'm new to react, and I'm guessing this isn't allowed or something. But I'm trying to have the password page show until, its style is changed to "none", which happens in a different component. function App() { const [loggedIn, setLoggedIn] = useState(false) if (document.getElementById('password').style.display = "block"){ setLoggedIn(false) } else { setLoggedIn(true) }

问题 I tried to track the number of times react component is rendered. However, it seems that the renderCounter gets incremented by 2 each time. Why does this happen? I know it is a bad practice to use global variables, but I'm interested in the reason why this happens. https://codesandbox.io/s/rendercounter-does-not-increment-correctly-093ok?file=/src/App.js let renderCounter = 1; function App() { const [i, inc] = useReducer((_) => _ + 1, 1); // render console.log(JSON.stringify(i), "th click");

问题 I tried to track the number of times react component is rendered. However, it seems that the renderCounter gets incremented by 2 each time. Why does this happen? I know it is a bad practice to use global variables, but I'm interested in the reason why this happens. https://codesandbox.io/s/rendercounter-does-not-increment-correctly-093ok?file=/src/App.js let renderCounter = 1; function App() { const [i, inc] = useReducer((_) => _ + 1, 1); // render console.log(JSON.stringify(i), "th click");