frontend/js/common/dom/dynamic_content_updater.js

/**
 * Update root's child element to be newElementTag replacing another existing child if any.
 * Copy attributes into the child element.
 */
export default function dynamicContentUpdater(root, newElementTag, attributes) {
  const rootEl = root;
  let customEl;

  if (rootEl.lastChild && rootEl.lastChild.tagName === newElementTag) {
    customEl = rootEl.lastChild;
  } else {
    if (rootEl.lastChild) {
      rootEl.removeChild(rootEl.lastChild);
    }
    // Creating an element with upper case works fine in Chrome, but in FF it doesn't immediately
    // become a defined Custom Element. Polymer does that in some later pass.
    customEl = document.createElement(newElementTag.toLowerCase());
  }

  if (customEl.setProperties) {
    customEl.setProperties(attributes);
  } else {
    // If custom element definition wasn't loaded yet - setProperties would be
    // missing, but no harm in setting attributes one-by-one then.
    Object.keys(attributes).forEach((key) => {
      customEl[key] = attributes[key];
    });
  }

  if (customEl.parentNode === null) {
    rootEl.appendChild(customEl);
  }
}