React - how to display current time with refresh

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In this article, we would like to show you how to display current time which is refreshed after some short time in React.

In below example, we use interval with a React.useEffect hook to build a simple timer. 
We don't want unnecessary function calls with the useEffect hook so we use a reference to the function (created with a React.useRef hook). When setInterval performs some operations every specified time, it refers to the function currently assigned to the reference, updating the time stored as a state. The function assigned to the reference is updated every render cycle.
The whole mechanism will be stopped when a component is destroyed (with the clearInterval function).

Note: Go to the next section of this article to read more about useCurrentCallback function.

Runnable example:

// ONLINE-RUNNER:browser;

//Note: Uncomment import lines during working with JSX Compiler.
// import React from 'react';
// import ReactDOM from 'react-dom';

const useCurrentCallback = (callback) => {
  const reference = React.useRef();
  reference.current = callback;
  return (...args) => {
    return reference.current?.(...args);

const App = () => {
  const [time, setTime] = React.useState(0);
  const currentCallback = useCurrentCallback(() => {
    const date = new Date();
  React.useEffect(() => {
    const handle = setInterval(currentCallback, 100);
    return () => clearInterval(handle);
  }, []);
  return (

const root = document.querySelector('#root');
ReactDOM.render(<App />, root);


useCurrentCallback function uses React.useRef hook to initialize reference.current with a callback function that updates our time with a new date.

The useCurrentCallback returns an arrow function with an unspecified number of arguments (...args). The arrow function returns a callback function stored in reference.current with all of the ...args if possible, otherwise returns undefined. 


Read more about date and time formatting here.

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