jscodes

--------------------------------------------------------------------------   import React , { useState , useEffect } from 'react' ; import axios from 'axios' const DataPull = () => { const [ id , setId ] = useState ( 1 ) const [ post , setPost ] = useState ({}) const [ buttonid , setButtonid ] = useState ( 1 ) const handleClick = () => { console . log ( "button id set" ) setButtonid ( id ) } useEffect (() => { console . log ( "normal id " + id ) console . log ( "button id " + buttonid ) axios . get ( `https://jsonplaceholder.typicode.com/posts/ ${ buttonid } ` ). then ( res => { setPost ( res . data ) }). catch ( err => { console . log ( err ) setPost ({ title : "no data" }) }) }, [ buttonid ]) return ( <div> <input type = "text" ...

import React, { useState, useEffect } from 'react'; import './App.css' const App = () => { const [cnt, setCnt] = useState(0) const [tmp, setTmp] = useState('10') useEffect(() => { document.title = `${cnt}` console.log("use effect called") },[cnt]) // only run useEffect when cnt value changes, condition applied on cnt return ( <div className="App"> <input type="text" onChange={(e) => { setTmp(e.target.value) console.log(e.target.value) }} /> "text {tmp} " <button onClick={() => setCnt(cnt + 1)}>Plus+</button> {cnt} </div> ); } export default App; //useEffect runs after every render of component sideeffect => any thing that reaches outside of component to do something eg . n / w request manual dom manipulation to modify other parts of dom event Listener , timeout and interval

i mport React, { useState } from 'react'; import './App.css' const App = () => { const [name, setName] = useState({ fname: '', lname: '' }) return ( <div className="App"> <form> <input type="text" value={name.fname} onChange= {(e) => setName((prevstate) => ({ ...prevstate, fname: e.target.value }))} /> Fname is {name.fname} <br /> <input type="text" value={name.lname} onChange= {(e) => setName((prevstate) => ({ ...prevstate, lname: e.target.value }))} /> Lname is {name.lname} </form> { JSON . stringify ( name ) } </div> ); } export default App; onChange= {(e) => setName((prevstate) => ({ ...prevstate, lname: e.target.value }))} the ...prevstate above will merge current state to previous state #working with ARRAY import React , { useState } from 'react' ; import './App.css' const App = () => { const [ items , setItems ] =...

. import React , { useState } from 'react' ; import './App.css' const App = () => { const [ count1 , setCount1 ] = useState ( 1 ) const [ count2 , setCount2 ] = useState ( 2 ) const [{ count3 , count4 }, setCount ] = useState ({ count3 : 8 , count4 : 9 }) return ( <div className = "App" > <button onClick = { () => { setCount1 ( c => c + 1 ) setCount2 ( c => c + 1 ) } } > Add-it </button> <div> count1= { count1 } </div> <div> count2= { count2 } </div> <button onClick = { () => { setCount (( c ) => ({ ... c , count3 : count3 + 100 , count4 : count4 + 100 }) ) //here "c" is currentstate and the ...c spreadoperator } } > add obj </button> <div> count3= { count3 } </div><div> count4= { count4 } </div> </div> ); } export def...

  const companies=[   {name:"facebook",start:"100",end:"110"}, {name:"amazon",start:"123",end:"321"},{name:"bamboo",start:"34",end:"45"}, {name:"netflix",start:"20",end:"223"} ] const ages = [31,21,11,3,15,32,53,34,15,76,79,84,91] //For each companies.forEach((item)=>{console.log(item["name"] + "..elements")}); output: facebook :elements amazon :elements // filter out ages that are below 21 (remove elements less than 21) //filter const canSmoke=ages.filter((age)=>(age> 21 )) console.log(canSmoke) const oldestCompany = companies.filter((comp)=>{ if (comp.end> 100 ){ return true ;} }) //console.log("The oldest is: " + JSON.stringify(oldestCompany)) console.log( "The oldest is: " + oldestCompany) oldestCompany.forEach(x=>console.log(x)) const eightiesCompany = companies.filter...