Check to see if the current tab is visible

checkPageVisibility.js

// CHECK TO SEE IF THE CURRENT TAB IS VISIBLE
// 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";
    console.log('I have been hidden');
    visibilityChange = "visibilitychange";
} else if (typeof document.mozHidden !== "undefined") {
    hidden = "mozHidden";
    console.log('Moz has been hidden');
    visibilityChange = "mozvisibilitychange";
} else if (typeof document.msHidden !== "undefined") {
    hidden = "msHidden";
    console.log('Ms has been hidden');
    visibilityChange = "msvisibilitychange";
} else if (typeof document.webkitHidden !== "undefined") {
    hidden = "webkitHidden";
    console.log('Webkit has been hidden');
    visibilityChange = "webkitvisibilitychange";
}
// IF CURRENT TAB BECOMES VISIBLE AGAIN, DO SOMETHING
if (typeof document.addEventListener !== "undefined" ||
  typeof document[hidden] !== "undefined") {
  // Handle page visibility change
  document.addEventListener(visibilityChange, function(){
    if( document[hidden] ) {
        console.log('document hidden');
    } else {
        console.log('document visible');
    }
  }, false);
}