Finds the common ancestor of nodes in a document. Useful for event delegation for example.

greatestCommonAncestor.js

/**
 * greatestCommonAncestor - Finds the common ancestor of nodes in a document.
 * The nodes MUST belong to the same document(fragment).
 * @param {...Node} nodes - The nodes whose common ancestor is sought.
 * @returns {Node} - The common ancestor to all nodes given as arguments.
 */
export function greatestCommonAncestor () {
  return Array.prototype.reduce.call(
    arguments, // partial application `?` when? :(
    (ancestor, node) => {
      if (node === ancestor)
        return ancestor;

      let mask = node.compareDocumentPosition(ancestor);

      // The current node contains the ancestor
      if (mask & Node.DOCUMENT_POSITION_CONTAINED_BY)
        return node;

      // The ancestor contains the current node?
      while ((mask & Node.DOCUMENT_POSITION_CONTAINS) === 0) {
        // No: We find the closest parent of the ancestor that does
        ancestor = ancestor.parentNode;
        mask = node.compareDocumentPosition(ancestor);
      }

      return ancestor;
    }
  );
}

// Use
const parent = greatestCommonAncestor(input1, input2, input3);
parent.addEventListener("click", (evt) => {
  switch (evt.target) {
    case input1:
      ...
  }
}, false);