Check if window has focus

Why not use the hasFocus method e.g.

if (document.hasFocus()) {
    ...
}

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If you need to handle iframe's as well then your check just becomes either or e.g.

function isFocused() {
    return document.hasFocus() || document.getElementById('iframe').contentWindow.document.hasFocus();
}

You can use document.visibilityState to know whether the page is in focus or not.