livebook/assets/js/morphdom_callbacks.js

const callbacks = {
  onBeforeElUpdated(from, to) {
    // Keep element attributes starting with data-js-
    // which we set on the client.
    for (const attr of from.attributes) {
      if (attr.name.startsWith("data-js-")) {
        to.setAttribute(attr.name, attr.value);
      }
    }
  },

  onNodeAdded(node) {
    // Mimic autofocus for dynamically inserted elements
    if (node.nodeType === Node.ELEMENT_NODE && node.hasAttribute("autofocus")) {
      node.focus();

      if (node.setSelectionRange && node.value) {
        const lastIndex = node.value.length;
        node.setSelectionRange(lastIndex, lastIndex);
      }
    }
  },
};

export default callbacks;