axe-core/lib/core/utils/get-scroll.js

Accessibility engine for automated Web UI testing

/**
 * Get the scroll position of given element
 * @method getScroll
 * @memberof axe.utils
 * @param {Element} node
 * @param {buffer} (Optional) allowed negligence in overflow
 * @returns {Object | undefined}
 */
function getScroll(elm, buffer = 0) {
  const overflowX = elm.scrollWidth > elm.clientWidth + buffer;
  const overflowY = elm.scrollHeight > elm.clientHeight + buffer;

  /**
   * if there is neither `overflow-x` or `overflow-y`
   * -> return
   */
  if (!(overflowX || overflowY)) {
    return;
  }

  const style = window.getComputedStyle(elm);
  const overflowXStyle = style.getPropertyValue('overflow-x');
  const overflowYStyle = style.getPropertyValue('overflow-y');
  const scrollableX =
    overflowXStyle !== 'visible' && overflowXStyle !== 'hidden';
  const scrollableY =
    overflowYStyle !== 'visible' && overflowYStyle !== 'hidden';

  /**
   * check direction of `overflow` and `scrollable`
   */
  if ((overflowX && scrollableX) || (overflowY && scrollableY)) {
    return {
      elm,
      top: elm.scrollTop,
      left: elm.scrollLeft
    };
  }
}

export default getScroll;