ckknight ckknight - 7 months ago 27
Javascript Question

How to tell if browser/tab is active


Possible Duplicate:

Is there a way to detect if a browser window is not currently active?




I have a function that is called every second that I only want to run if the current page is in the foreground, i.e. the user hasn't minimized the browser or switched to another tab. It serves no purpose if the user isn't looking at it and is potentially CPU-intensive, so I don't want to just waste cycles in the background.

Does anyone know how to tell this in JavaScript?

Note: I use jQuery, so if your answer uses that, that's fine :).

Answer

You would use the focus and blur events of the window:

var interval_id;
$(window).focus(function() {
    if (!interval_id)
        interval_id = setInterval(hard_work, 1000);
});

$(window).blur(function() {
    clearInterval(interval_id);
    interval_id = 0;
});

To Answer the Commented Issue of "Double Fire" and stay within jQuery ease of use:

$(window).on("blur focus", function(e) {
    var prevType = $(this).data("prevType");

    if (prevType != e.type) {   //  reduce double fire issues
        switch (e.type) {
            case "blur":
                // do work
                break;
            case "focus":
                // do work
                break;
        }
    }

    $(this).data("prevType", e.type);
})

Click to view Example Code Showing it working (JSFiddle)