src/ResizeSensor.js
function() {
          if ((cachedWidth = element.offsetWidth) != lastWidth || (cachedHeight = element.offsetHeight) != lastHeight) {
              dirty = true;

              lastWidth = cachedWidth;
              lastHeight = cachedHeight;
          }
          reset();
        }
function() {
          if ((cachedWidth = element.offsetWidth) != lastWidth || (cachedHeight = element.offsetHeight) != lastHeight) {
              dirty = true;

              lastWidth = cachedWidth;
              lastHeight = cachedHeight;
          }
          reset();
        }
useful to not query offsetWidth twice