Page Visibility.js

// Instance of Ad
var banner = new Ad(params)

// Set the name of the hidden property and the change event for visibility
var hidden, visibilityChange; 

if (typeof document.hidden !== "undefined") { // Opera 12.10 and Firefox 18 and later support 
    hidden = "hidden";
    visibilityChange = "visibilitychange";
} else if (typeof document.msHidden !== "undefined") {
    hidden = "msHidden";
    visibilityChange = "msvisibilitychange";
} else if (typeof document.webkitHidden !== "undefined") {
    hidden = "webkitHidden";
    visibilityChange = "webkitvisibilitychange";
}

// If the page is hidden, pause tracking impressions
// if the page is shown, resume tracking impressions
function handleVisibilityChange() {
    if (document[hidden]) {
        banner.pause()
    } else {
        banner.resume()
    }
}

// Warn if the browser doesn't support addEventListener or the Page Visibility API
if (typeof document.addEventListener === "undefined" || hidden === undefined) {
    console.log("This SDK requires a browser, such as Google Chrome or Firefox, that supports the Page Visibility API.");
} else {
    // Handle page visibility change   
    document.addEventListener(visibilityChange, handleVisibilityChange, false);
}