Detect which tab/window is being focused in Google Chrome

Question

I'm making a Chrome extension that contains a content script that does the following:

• the content script is injected into every page
• periodically calls function "a" every 5 seconds
• if the page is in focus, it calls function "b".

Ideally, function "a" should be called for every tab, but function "b" will only be called for the tab that is focused.

I've looked into several ways of doing this, the closest solution I've found is this: How to detect when a tab is focused or not in Chrome with Javascript?

However, when I tried to use the outerHeight/innerHeight method, it gave me some really weird results. When the window is out of focus, I get 0 for outerHeight. Which seems more like a bug to me, so I'm not sure if I can use this to determine whether the tab is out of focus or not.

Does anyone have a good solution for this?

Answer 1

Don't know a content script only solution, but this can be easily done with help of background page:

content_script.js:

function task() {
    chrome.extension.sendRequest("is_selected", function(isSelected) {
        if(isSelected) {
            //this tab in focus
        } else {
            //not in focus
        }
    });
}
setInterval(task, 5000);

background.html:

chrome.extension.onRequest.addListener(function(request, sender, sendResponse) {
    if(request == "is_selected") {
        chrome.tabs.getSelected(null, function(tab){
            if(tab.id == sender.tab.id) {
                sendResponse(true); //in focus (selected)
            } else {
                sendResponse(false);    //not in focus
            }
        });
    }
});