How come the focus doesn't work when altering the CSS code simultaneously?

My attempt at creating a user interface involved an issue where the input field was not visible initially. After clicking the button, the input would appear on the screen, and I wanted to automatically focus on it.


This is what I tried to achieve: Initially, the parent component of the input had its display property set to 'none', hiding the input from view. When the button was clicked, this property was changed to 'block', revealing the input. My intention was to set focus on the input simultaneously, but my initial approach did not work as expected. Let me share the code with you:


const [inputDisplay, setInputDisplay] = useState("none");
const refInput = useRef(null);

const HandleShowInput = () => {
  setInputDisplay("block");
  refInput.current.focus();
};

return (
  <>
    <Box theme={inputDisplay}>
      <Input ref={refInput}/>
    <Box/>
    <Button onClick={HandleShowInput}/>
  </>
)

The above code did not produce the desired result. However, when I moved the focus-setting logic inside a useEffect hook, it worked successfully. Here is the revised code:


const [inputDisplay, setInputDisplay] = useState("none");
const refInput = useRef(null);

const HandleShowInput = () => {
  setInputDisplay("block");
};

useEffect(() => {
    refInput.current.focus();
}, [inputDisplay]);

return (
  <>
    <Box theme={inputDisplay}>
      <Input ref={refInput}/>
    <Box/>
    <Button onClick={HandleShowInput}/>
  </>
)

I am seeking insight into why the first approach failed while the second one succeeded. It is possible that I am lacking in either React or CSS knowledge. As a beginner in React development, your guidance would be greatly appreciated. Thank you for understanding any language barriers or awkward phrasing in my explanation.

Answer ā„–1

When utilizing the HandleShowInput function to focus on the input element, two key actions take place simultaneously: state alteration and focusing the input. However, due to the swift nature of these actions, the input may be focused too quickly for it to be visible on the user interface. Additionally, as a result of the state change triggering a re-render, the ref will once again grab the input element, rendering the focused input invisible.

On the flip side, when employing useEffect, the focusing occurs after the initial render with no subsequent renders, allowing us to view the focused input clearly.

Answer ā„–2

When it comes to React, the approach is slightly different compared to Javascript.

You might assume that the following two will behave similarly:

 setInputDisplay("block");
  refInput.current.focus();

and

document.querySelector('#canFocus').style.display='block'
document.querySelector('#canFocus').focus();

However, that's not the case. In Javascript, the DOM is first blocked and then focused, which functions effectively. But in React, it operates differently as shown in the code snippet below.

setTimeout(()=>{
  // next react render cycle callback
  document.querySelector('#canNotFocus').style.display='block'
}, 1000)
document.querySelector('#canNotFocus').focus();

Upon calling the focus method, the DOM is initially displayed as none. Upon setting state in React, ReactDOM will change it to display block in the subsequent lifecycle of the function component. You can view a demo here.

useEffect(() => {
    refInput.current.focus();
}, [inputDisplay]);

This is a monitoring function. When inputDisplay changes, the enclosed function will be triggered.

  1. You set the state to block
  2. React re-renders the component based on the new state
  3. The render function is executed, and the DOM becomes visible
  4. The effect-watching function is invoked, resulting in a call to focus()

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