Check if the browser tab is in focus in ReactJS

I found This library. It could be of help.

Here's how I would use it to solve your problem

import React from 'react';
import PageVisibility from 'react-page-visibility';

class YourComponent extends React.Component {
    state = {
      isWindowInFocus: true,
    }
    componentDidMount() {
      const { isWindowInFocus } = this.props;
      if (!isWindowInFocus) {
        // do something
      }
    }

    listentoWindow = isVisible => {
      this.setState({
        isWindowInFocus: isVisible,
      });
    }
    render() {
      return (
        <PageVisibility onChange={this.listentoWindow}>
          <div>
           Your component JSX
          </div>
        </PageVisibility>
      );
    }
}

This should work:

componentDidMount() {
    window.addEventListener("focus", this.onFocus)
}

componentWillUnmount() {
    window.removeEventListener("focus", this.onFocus)
}

onFocus = () => {
    //
}

Edit: same goes for "blur" and it should work for when the tab becomes hidden.

Check @Assaf's answer for usage with hooks.

There is no reliable method to check it, so you need to combine few methods together. Here is Context for react-hooks

import React, { useState, useEffect } from 'react'

export const WindowContext = React.createContext(null)

export const WindowContextProvider = props => {
  const [windowIsActive, setWindowIsActive] = useState(true)


  function handleActivity(forcedFlag) {
    if (typeof forcedFlag === 'boolean') {
      return forcedFlag ? setWindowIsActive(true) : setWindowIsActive(false)
    }

    return document.hidden ? setWindowIsActive(false) : setWindowIsActive(true)
  }

  useEffect(() => {
    const handleActivityFalse = () => handleActivity(false)
    const handleActivityTrue = () => handleActivity(true)

    document.addEventListener('visibilitychange', handleActivity)
    document.addEventListener('blur', handleActivityFalse)
    window.addEventListener('blur', handleActivityFalse)
    window.addEventListener('focus', handleActivityTrue )
    document.addEventListener('focus', handleActivityTrue)

    return () => {
      window.removeEventListener('blur', handleActivity)
      document.removeEventListener('blur', handleActivityFalse)
      window.removeEventListener('focus', handleActivityFalse)
      document.removeEventListener('focus', handleActivityTrue )
      document.removeEventListener('visibilitychange', handleActivityTrue )
    }
  }, [])

  return <WindowContext.Provider value={{ windowIsActive }}>{props.children}</WindowContext.Provider>
}

Just built this using hooks as of React 16.8

import React, { useEffect } from "react";

// User has switched back to the tab
const onFocus = () => {
    console.log("Tab is in focus");
};

// User has switched away from the tab (AKA tab is hidden)
const onBlur = () => {
    console.log("Tab is blurred");
};

const WindowFocusHandler = () => {
    useEffect(() => {
        window.addEventListener("focus", onFocus);
        window.addEventListener("blur", onBlur);
        // Calls onFocus when the window first loads
        onFocus();
        // Specify how to clean up after this effect:
        return () => {
            window.removeEventListener("focus", onFocus);
            window.removeEventListener("blur", onBlur);
        };
  }, []);

    return <></>;
};

export default WindowFocusHandler;