Function observer

examples/js/processing.js:5273–5280

(obj, event, handler)

          },

          observer = function(obj, event, handler) {
            if (obj.addEventListener) {
              obj.addEventListener(event, handler, False);
            } else if (obj.attachEvent) {
              obj.attachEvent("on" + event, handler);
            }
            return [obj, event, handler];
          },
          unobserve = function(obj, event, handler) {
            if (obj.removeEventListener) {
              obj.removeEventListener(event, handler, False);