[Solved]-React hook useState not updating onclick-Reactjs

useState hook is asynchronous, and will not be reflected immediately.. try this:

  useEffect(() => {
    
    }, [SidebarClass]);

I think you add useEffect hooks to check I explain briefly what did you wrong when you click your close button closed handler function trigger and setState function calling at the same time(asynchronous) console.log statement printed. //'side bar'

in your code, you can't verify your state change or not (only you can verify from the render method) because the closed handler function triggers only one time if you want to check your className is changed or not from console.log statement you must need useEffect hook it will trigger every time after your state changed so can conform it your className is changed or not

//only trigger one time 
 useEffect(()=>{
 console.log(SidebarClass);//output 'sidebar'
 },[])
        
 //hooks trigger every time after your state changed
  useEffect(()=>{
 console.log(SidebarClass); 
 //output 'sidebar' 
 //output user-side-bar close
            })
        
 //only trigger if SidebarClass state changed
 useEffect(()=>{
 console.log(SidebarClass);
 //output 'sidebar' 
 //output user-side-bar close
 },[SidebarClass]);