focusinterval.js

/*!
 * @version 1.0
 * @see ORFON
 * A setInterval which is pausable and does not trigger
 * when the current document doesn't have focus.
 *
 * Must explictely be `start()`ed.
 *
 * Optionally, the callback can return `false` in which case the
 * `interval` duration is increased in `intervalStep` up to `maxInterval` until a later callback
 * returns `true` at which point the `interval` is reset to `minInterval`.
 */

jQuery(function($) {

   $.FocusInterval = function(func) {
      // const
      var minInterval = 10;
      var maxInterval = 1800
      var intervalStep = 10,

      // var
      var isPaused = true;
      var interval = 10,

      var tick = function() {
         // if we don't have focus or we are paused -> check again later
         if (isPaused || !document.hasFocus()) {
            window.setTimeout(tick, minInterval * 1000);
            return;
         }

         var returnValue = options.func();
         if (returnValue === false) {
            interval = Math.min(interval + intervalStep, maxInterval);
         }
         if (returnValue === true) {
            interval = minInterval;
         }
         window.setTimeout(tick, interval * 1000);
      }
      tick();

      return {
         stop: function() {
            isPaused = true;
         },
         start: function() {
            isPaused = false;
         },
      }
   }
});