Detect browser focus/out-of-focus via Google Chrome Extension

You can use the chrome.windows API to monitor this. You would add a listener for the onFocusChanged event and if the event returned -1 or chrome.windows.WINDOW_ID_NONE then you know that the browser lost focus:

var inFocus = true;  // global boolean to keep track of statechrome.windows.onFocusChanged.addListener(function(window) {    if (window == chrome.windows.WINDOW_ID_NONE) {        inFocus = false;    } else {        inFocus = true;    }});

Chrome.Window Doc

Maybe some don't see @Giedrius' comment. This interval works:

window.setInterval(checkBrowserFocus, 1000);  function checkBrowserFocus(){    chrome.windows.getCurrent(function(browser){      console.log(browser.focused)    })}

setInterval(function() {    chrome.windows.getLastFocused(function(window) {        console.log(window.id.toString() + "  " + window.focused.toString())    });}, 1000);

or：

setInterval(function() {    chrome.windows.getCurrent(function(window) {        console.log(window.id.toString() + "  " + window.focused.toString())    });}, 1000);

window.focused is false means that no chrome window is focused.

reference：https://developer.chrome.com/extensions/windows