cob-uswds/packages/uswds-core/src/js/utils/is-in-viewport.js

Customized USWDS UI components and visual style guide based on City of Boston Patterns Library

// https://stackoverflow.com/a/7557433
function isElementInViewport(
  el,
  win = window,
  docEl = document.documentElement,
) {
  const rect = el.getBoundingClientRect();

  return (
    rect.top >= 0 &&
    rect.left >= 0 &&
    rect.bottom <= (win.innerHeight || docEl.clientHeight) &&
    rect.right <= (win.innerWidth || docEl.clientWidth)
  );
}

module.exports = isElementInViewport;