google analytics - Is there a way track the focus on tab with Javascript?

Question

• We need to track the EFFECTIVE time on site of our users
• Most users, when they're done, leave the tab open and move to another tab
• Time on site it's extremely inaccurate

Is there a Javascript Event to track the "loss of focus" of the current tab ?

Answer 1

This should work both on tab switch and on browser window losing focus:

function onBlur() {
    document.body.className = 'blurred';
};
function onFocus(){
    document.body.className = 'focused';
};

if (/*@cc_on!@*/false) { // check for Internet Explorer
    document.onfocusin = onFocus;
    document.onfocusout = onBlur;
} else {
    window.onfocus = onFocus;
    window.onblur = onBlur;
}