materialize-css/js/scrollFire.js

(function($) {

  var scrollFireEventsHandled = false;

  // Input: Array of JSON objects {selector, offset, callback}
  Materialize.scrollFire = function(options) {
    var onScroll = function() {
      var windowScroll = window.pageYOffset + window.innerHeight;

      for (var i = 0 ; i < options.length; i++) {
        // Get options from each line
        var value = options[i];
        var selector = value.selector,
            offset = value.offset,
            callback = value.callback;

        var currentElement = document.querySelector(selector);
        if ( currentElement !== null) {
          var elementOffset = currentElement.getBoundingClientRect().top + window.pageYOffset;

          if (windowScroll > (elementOffset + offset)) {
            if (value.done !== true) {
              if (typeof(callback) === 'function') {
                callback.call(this, currentElement);
              } else if (typeof(callback) === 'string') {
                var callbackFunc = new Function(callback);
                callbackFunc(currentElement);
              }
              value.done = true;
            }
          }
        }
      }
    };


    var throttledScroll = Materialize.throttle(function() {
      onScroll();
    }, options.throttle || 100);

    if (!scrollFireEventsHandled) {
      window.addEventListener("scroll", throttledScroll);
      window.addEventListener("resize", throttledScroll);
      scrollFireEventsHandled = true;
    }

    // perform a scan once, after current execution context, and after dom is ready
    setTimeout(throttledScroll, 0);
  };

})(jQuery);