tomekwi/mithril-n

import m from 'mithril';

export default function n () {

  // First, let Mithril process our arguments and generate a `view`.
  let view = m.apply(null, arguments);
  let config = view.attrs.config;

  // Divide `view.children` nodes between DOM and vDOM. Save all as a flat array
  // in `kids`.
  let kids = [];
  let dom = [];
  let vdom = [];
  view.children.forEach(function recurse (kid) {

    // - push the child where it belongs, if it's not an array
    if (!(kid instanceof Array)) {
      kids.push(kid);
      (kid instanceof Node ? dom : vdom).push(kid);
      return;
    }

    // - and if it is an array, recurse these steps over each of its items
    kid.forEach(recurse);  // (when TCO comes, we should be ready for it)
  });

  // If we have DOM nodes among the `view.children`,
  if (dom.length) {

    // leave just vDOM nodes among children
    view.children = vdom;

    // and override the view's `config` attribute with the following function:
    view.attrs.config = function appendDOM (element) {

      // - add every DOM node to the view's root element – its position is
      //   determined by the node's original position in `kids`
      for (let node of dom) {
        element.insertBefore(node,
          element.childNodes[kids.indexOf(node)] || null
        );
      }

      // - call the original `config` function
      return config && config.apply(null, arguments);
    };
  }

  // Return the view, ready for rendering.
  return view;
}