atom-dom.js

const seq = (...args) => input => args.reduce((acc, el) => el(acc), input)
const cons = (a, b) => fn => fn(b == null ? b : a, b || a)
const car = pair => pair((a, b) => a)
const cdr = pair => pair((a, b) => b)
const tree = comp => seq(car(comp), cdr(comp))
const isCons = fn => fn.toString() === 'fn => fn(b == null ? b : a, b || a)'

;((win, doc) => {

  const tags = ["a", "abbr", "acronym", "address", "applet", "area", "article", "aside", "audio", "b", "base", "basefont", "bdi", "bdo", "big", "blockquote", "body", "br", "button", "canvas", "caption", "center", "cite", "code", "col", "colgroup", "data", "datalist", "dd", "del", "details", "dfn", "dialog", "dir", "div", "dl", "dt", "em", "embed", "fieldset", "figcaption", "figure", "font", "footer", "form", "frame", "frameset", "h1", "h2", "h3", "h4", "h5", "h6", "head", "header", "hr", "html", "i", "iframe", "img", "input", "ins", "kbd", "keygen", "label", "legend", "li", "link", "main", "map", "mark", "menu", "menuitem", "meta", "meter", "nav", "noframes", "noscript", "object", "ol", "optgroup", "option", "output", "p", "param", "picture", "pre", "progress", "q", "rp", "rt", "ruby", "s", "samp", "script", "section", "select", "small", "source", "span", "strike", "strong", "style", "sub", "summary", "sup", "table", "tbody", "td", "textarea", "tfoot", "th", "thead", "time", "title", "tr", "track", "tt", "u", "ul", "var", "video"]
  const attributeExceptions = ['role', 'attribute']
  const eventExceptions = ['onClick']

  const childAppender = (win, doc, parent, child) => {
    if (Array.isArray(child)) {
      child.reduce(childAppender.bind(null, win, doc), parent)
    } else if (child instanceof win.Element) {
      parent.appendChild(child)
    } else if (typeof child === 'string') {
      parent.appendChild(doc.createTextNode(child))
    }
    return parent
  }

  const setStyles = (el, styles) => {
    if (!styles) {
      el.removeAttribute('styles')
      return el
    }
    Object.keys(styles)
      .map((prop) => {
        if (prop in el.style) {
          el.style[prop] = styles[prop]
        } else {
          console.warn(`${styleName} is not a valid style for a <${el.tagName.toLowerCase()}>`);
        }
      })
    return el
  }

  const setAttributes = (el, attrs) => {
    Object.keys(attrs)
      .map((prop) => {
        if (attrs[prop] === undefined) {
          el.removeAttribute(prop)
        } else {
          el.setAttribute(prop, attrs[prop])
        }
      })
    return el
  }

  const createElement = (win, doc, type, textOrPropsOrChild, ...otherChildren) => {
    const el = doc.createElement(type)
    const appendChild = childAppender.bind(null, win, doc)

    if (Object.prototype.toString.apply(textOrPropsOrChild) === '[object Object]') {
    	console.log(textOrPropsOrChild)
      Object.keys(textOrPropsOrChild)
        .map((name) => {
          if (name in el || attributeExceptions.includes(name)) {
            const value = textOrPropsOrChild[name]
            if (name === 'style') {
              setStyles(el, value)
            } else if (name === 'attribute') {
              setAttributes(el, value)
            } else if (value) {
              el[name] = value
            }
          } else if (eventExceptions.includes(name)) {
            const eventName = name.slice(2).toLowerCase()
            el.addEventListener(eventName, textOrPropsOrChild[name])
          } else {
            console.warn(`${name} is not a valid property of a <${type}>`)
          }
        })
    } else if (isCons(textOrPropsOrChild)) {
    	const component = tree(textOrPropsOrChild)(store.getState())
      console.log(component)
      appendChild(el, component)
    } else {
      appendChild(el, textOrPropsOrChild)
    }

    if (otherChildren) appendChild(el, otherChildren)
    return el
  }

  win.domjs = tags.reduce((acc, tag) => {
    acc[tag] = createElement.bind(null, win, doc, tag)
    return acc
  }, {})

})(window, document)

function createStore (reducers, initialState) {
  if (typeof reducers === 'function') {
    reducers = [reducers]
  }
  var listeners = []
  var state = initialState

  reducers.push(function setStateReducer (action, state) {
    return action && action.type === '__ATOM_SET_STATE__'
      ? Object.assign(state, action.payload)
    : state
  })

  return {
    addReducer: addReducer,
    removeReducer: removeReducer,
    dispatch: dispatch,
    subscribe: subscribe,
    unsubscribe: unsubscribe,
    getState: getState,
    setState: setState
  }

  function addReducer (reducer) {
    if (typeof reducer !== 'function') {
      throw new E('reducer must be a function')
    }
    reducers.push(reducer)
  }

  function removeReducer (reducer) {
    if (!reducer) return
    const idx = reducers.findIndex(l => l === reducer)
    idx > -1 && reducers.splice(idx, 1)
  }

  function dispatch (/* action[, action1, action2, ...] */) {
    var len = arguments.length
    var newState = getState()
    for (var x = 0; x < len; x++) {
      newState = callReducers(reducers, arguments[x], newState)
    }
    if (validState(newState)) {
      cb(newState)
    }
  }

  function subscribe (listener) {
    if (typeof listener !== 'function') {
      throw new E('listener must be a function')
    }
    listeners.push(listener)
    return function () { unsubscribe(listener) }
  }

  function unsubscribe (listener) {
    if (!listener) return
    const idx = listeners.findIndex(l => l === listener)
    idx > -1 && listeners.splice(idx, 1)
  }

  function getState () {
    return typeof state === 'object'
      ? Object.assign({}, state)
    : state
  }

  function setState (newState) {
    dispatch({type: '__ATOM_SET_STATE__', payload: newState})
  }

  // Private

  function callReducers (fns, action, state) {
    var newState = state
    var len = reducers.length
    var ret
    for (var x = 0; x < len; x++) {
      ret = fns[x](action, newState)
      if (validState(ret)) {
        newState = ret
      }
    }
    return newState
  }

  function cb (newState) {
    state = newState
    for (var x = 0; x < listeners.length; x++) {
      listeners[x]()
    }
  }

  function validState (newState) {
    if (newState === undefined) {
      throw new E('Reducer must return a value.')
    } else if (typeof newState.then === 'function') {
      throw new E('Reducer cannot return a Promise.')
    } else if (typeof newState === 'function') {
      newState(dispatch)
    } else {
      return true
    }
  }

  function E (message) {
    this.message = message
    this.name = 'AtomException'
    this.toString = function () {
      return this.name + ': ' + this.message
    }
  }
}

const {div, h1, button} = domjs

const mount = (node, comp, store) => {
	const el = tree(comp)(store.getState())
	node.appendChild(el)
  const patch = () => morphdom(el, tree(comp)(store.getState()))
  store.subscribe(patch)
	return patch
}

// userland

const store = createStore([], {count: 1})
const set = store.setState
const get = store.getState

const btn = cons(() =>
	button({onClick: () => set({count: get().count + 1})}, 'click me'))

const app = cons(state => state.count, count =>
	div({className: 'wrapper'},
    h1(`Count ${count}`),
    btn
  ))
  
mount(document.getElementById('root'), app, store)

morphdom.js

(function (global, factory) {
    typeof exports === 'object' && typeof module !== 'undefined' ? module.exports = factory() :
    typeof define === 'function' && define.amd ? define(factory) :
    (global = global || self, global.morphdom = factory());
}(this, function () { 'use strict';

    var DOCUMENT_FRAGMENT_NODE = 11;

    function morphAttrs(fromNode, toNode) {
        var toNodeAttrs = toNode.attributes;
        var attr;
        var attrName;
        var attrNamespaceURI;
        var attrValue;
        var fromValue;

        // document-fragments dont have attributes so lets not do anything
        if (toNode.nodeType === DOCUMENT_FRAGMENT_NODE || fromNode.nodeType === DOCUMENT_FRAGMENT_NODE) {
          return;
        }

        // update attributes on original DOM element
        for (var i = toNodeAttrs.length - 1; i >= 0; i--) {
            attr = toNodeAttrs[i];
            attrName = attr.name;
            attrNamespaceURI = attr.namespaceURI;
            attrValue = attr.value;

            if (attrNamespaceURI) {
                attrName = attr.localName || attrName;
                fromValue = fromNode.getAttributeNS(attrNamespaceURI, attrName);

                if (fromValue !== attrValue) {
                    if (attr.prefix === 'xmlns'){
                        attrName = attr.name; // It's not allowed to set an attribute with the XMLNS namespace without specifying the `xmlns` prefix
                    }
                    fromNode.setAttributeNS(attrNamespaceURI, attrName, attrValue);
                }
            } else {
                fromValue = fromNode.getAttribute(attrName);

                if (fromValue !== attrValue) {
                    fromNode.setAttribute(attrName, attrValue);
                }
            }
        }

        // Remove any extra attributes found on the original DOM element that
        // weren't found on the target element.
        var fromNodeAttrs = fromNode.attributes;

        for (var d = fromNodeAttrs.length - 1; d >= 0; d--) {
            attr = fromNodeAttrs[d];
            attrName = attr.name;
            attrNamespaceURI = attr.namespaceURI;

            if (attrNamespaceURI) {
                attrName = attr.localName || attrName;

                if (!toNode.hasAttributeNS(attrNamespaceURI, attrName)) {
                    fromNode.removeAttributeNS(attrNamespaceURI, attrName);
                }
            } else {
                if (!toNode.hasAttribute(attrName)) {
                    fromNode.removeAttribute(attrName);
                }
            }
        }
    }

    var range; // Create a range object for efficently rendering strings to elements.
    var NS_XHTML = 'http://www.w3.org/1999/xhtml';

    var doc = typeof document === 'undefined' ? undefined : document;
    var HAS_TEMPLATE_SUPPORT = !!doc && 'content' in doc.createElement('template');
    var HAS_RANGE_SUPPORT = !!doc && doc.createRange && 'createContextualFragment' in doc.createRange();

    function createFragmentFromTemplate(str) {
        var template = doc.createElement('template');
        template.innerHTML = str;
        return template.content.childNodes[0];
    }

    function createFragmentFromRange(str) {
        if (!range) {
            range = doc.createRange();
            range.selectNode(doc.body);
        }

        var fragment = range.createContextualFragment(str);
        return fragment.childNodes[0];
    }

    function createFragmentFromWrap(str) {
        var fragment = doc.createElement('body');
        fragment.innerHTML = str;
        return fragment.childNodes[0];
    }

    /**
     * This is about the same
     * var html = new DOMParser().parseFromString(str, 'text/html');
     * return html.body.firstChild;
     *
     * @method toElement
     * @param {String} str
     */
    function toElement(str) {
        str = str.trim();
        if (HAS_TEMPLATE_SUPPORT) {
          // avoid restrictions on content for things like `<tr><th>Hi</th></tr>` which
          // createContextualFragment doesn't support
          // <template> support not available in IE
          return createFragmentFromTemplate(str);
        } else if (HAS_RANGE_SUPPORT) {
          return createFragmentFromRange(str);
        }

        return createFragmentFromWrap(str);
    }

    /**
     * Returns true if two node's names are the same.
     *
     * NOTE: We don't bother checking `namespaceURI` because you will never find two HTML elements with the same
     *       nodeName and different namespace URIs.
     *
     * @param {Element} a
     * @param {Element} b The target element
     * @return {boolean}
     */
    function compareNodeNames(fromEl, toEl) {
        var fromNodeName = fromEl.nodeName;
        var toNodeName = toEl.nodeName;

        if (fromNodeName === toNodeName) {
            return true;
        }

        if (toEl.actualize &&
            fromNodeName.charCodeAt(0) < 91 && /* from tag name is upper case */
            toNodeName.charCodeAt(0) > 90 /* target tag name is lower case */) {
            // If the target element is a virtual DOM node then we may need to normalize the tag name
            // before comparing. Normal HTML elements that are in the "http://www.w3.org/1999/xhtml"
            // are converted to upper case
            return fromNodeName === toNodeName.toUpperCase();
        } else {
            return false;
        }
    }

    /**
     * Create an element, optionally with a known namespace URI.
     *
     * @param {string} name the element name, e.g. 'div' or 'svg'
     * @param {string} [namespaceURI] the element's namespace URI, i.e. the value of
     * its `xmlns` attribute or its inferred namespace.
     *
     * @return {Element}
     */
    function createElementNS(name, namespaceURI) {
        return !namespaceURI || namespaceURI === NS_XHTML ?
            doc.createElement(name) :
            doc.createElementNS(namespaceURI, name);
    }

    /**
     * Copies the children of one DOM element to another DOM element
     */
    function moveChildren(fromEl, toEl) {
        var curChild = fromEl.firstChild;
        while (curChild) {
            var nextChild = curChild.nextSibling;
            toEl.appendChild(curChild);
            curChild = nextChild;
        }
        return toEl;
    }

    function syncBooleanAttrProp(fromEl, toEl, name) {
        if (fromEl[name] !== toEl[name]) {
            fromEl[name] = toEl[name];
            if (fromEl[name]) {
                fromEl.setAttribute(name, '');
            } else {
                fromEl.removeAttribute(name);
            }
        }
    }

    var specialElHandlers = {
        OPTION: function(fromEl, toEl) {
            var parentNode = fromEl.parentNode;
            if (parentNode) {
                var parentName = parentNode.nodeName.toUpperCase();
                if (parentName === 'OPTGROUP') {
                    parentNode = parentNode.parentNode;
                    parentName = parentNode && parentNode.nodeName.toUpperCase();
                }
                if (parentName === 'SELECT' && !parentNode.hasAttribute('multiple')) {
                    if (fromEl.hasAttribute('selected') && !toEl.selected) {
                        // Workaround for MS Edge bug where the 'selected' attribute can only be
                        // removed if set to a non-empty value:
                        // https://developer.microsoft.com/en-us/microsoft-edge/platform/issues/12087679/
                        fromEl.setAttribute('selected', 'selected');
                        fromEl.removeAttribute('selected');
                    }
                    // We have to reset select element's selectedIndex to -1, otherwise setting
                    // fromEl.selected using the syncBooleanAttrProp below has no effect.
                    // The correct selectedIndex will be set in the SELECT special handler below.
                    parentNode.selectedIndex = -1;
                }
            }
            syncBooleanAttrProp(fromEl, toEl, 'selected');
        },
        /**
         * The "value" attribute is special for the <input> element since it sets
         * the initial value. Changing the "value" attribute without changing the
         * "value" property will have no effect since it is only used to the set the
         * initial value.  Similar for the "checked" attribute, and "disabled".
         */
        INPUT: function(fromEl, toEl) {
            syncBooleanAttrProp(fromEl, toEl, 'checked');
            syncBooleanAttrProp(fromEl, toEl, 'disabled');

            if (fromEl.value !== toEl.value) {
                fromEl.value = toEl.value;
            }

            if (!toEl.hasAttribute('value')) {
                fromEl.removeAttribute('value');
            }
        },

        TEXTAREA: function(fromEl, toEl) {
            var newValue = toEl.value;
            if (fromEl.value !== newValue) {
                fromEl.value = newValue;
            }

            var firstChild = fromEl.firstChild;
            if (firstChild) {
                // Needed for IE. Apparently IE sets the placeholder as the
                // node value and vise versa. This ignores an empty update.
                var oldValue = firstChild.nodeValue;

                if (oldValue == newValue || (!newValue && oldValue == fromEl.placeholder)) {
                    return;
                }

                firstChild.nodeValue = newValue;
            }
        },
        SELECT: function(fromEl, toEl) {
            if (!toEl.hasAttribute('multiple')) {
                var selectedIndex = -1;
                var i = 0;
                // We have to loop through children of fromEl, not toEl since nodes can be moved
                // from toEl to fromEl directly when morphing.
                // At the time this special handler is invoked, all children have already been morphed
                // and appended to / removed from fromEl, so using fromEl here is safe and correct.
                var curChild = fromEl.firstChild;
                var optgroup;
                var nodeName;
                while(curChild) {
                    nodeName = curChild.nodeName && curChild.nodeName.toUpperCase();
                    if (nodeName === 'OPTGROUP') {
                        optgroup = curChild;
                        curChild = optgroup.firstChild;
                    } else {
                        if (nodeName === 'OPTION') {
                            if (curChild.hasAttribute('selected')) {
                                selectedIndex = i;
                                break;
                            }
                            i++;
                        }
                        curChild = curChild.nextSibling;
                        if (!curChild && optgroup) {
                            curChild = optgroup.nextSibling;
                            optgroup = null;
                        }
                    }
                }

                fromEl.selectedIndex = selectedIndex;
            }
        }
    };

    var ELEMENT_NODE = 1;
    var DOCUMENT_FRAGMENT_NODE$1 = 11;
    var TEXT_NODE = 3;
    var COMMENT_NODE = 8;

    function noop() {}

    function defaultGetNodeKey(node) {
      if (node) {
          return (node.getAttribute && node.getAttribute('id')) || node.id;
      }
    }

    function morphdomFactory(morphAttrs) {

        return function morphdom(fromNode, toNode, options) {
            if (!options) {
                options = {};
            }

            if (typeof toNode === 'string') {
                if (fromNode.nodeName === '#document' || fromNode.nodeName === 'HTML') {
                    var toNodeHtml = toNode;
                    toNode = doc.createElement('html');
                    toNode.innerHTML = toNodeHtml;
                } else {
                    toNode = toElement(toNode);
                }
            }

            var getNodeKey = options.getNodeKey || defaultGetNodeKey;
            var onBeforeNodeAdded = options.onBeforeNodeAdded || noop;
            var onNodeAdded = options.onNodeAdded || noop;
            var onBeforeElUpdated = options.onBeforeElUpdated || noop;
            var onElUpdated = options.onElUpdated || noop;
            var onBeforeNodeDiscarded = options.onBeforeNodeDiscarded || noop;
            var onNodeDiscarded = options.onNodeDiscarded || noop;
            var onBeforeElChildrenUpdated = options.onBeforeElChildrenUpdated || noop;
            var childrenOnly = options.childrenOnly === true;

            // This object is used as a lookup to quickly find all keyed elements in the original DOM tree.
            var fromNodesLookup = Object.create(null);
            var keyedRemovalList = [];

            function addKeyedRemoval(key) {
                keyedRemovalList.push(key);
            }

            function walkDiscardedChildNodes(node, skipKeyedNodes) {
                if (node.nodeType === ELEMENT_NODE) {
                    var curChild = node.firstChild;
                    while (curChild) {

                        var key = undefined;

                        if (skipKeyedNodes && (key = getNodeKey(curChild))) {
                            // If we are skipping keyed nodes then we add the key
                            // to a list so that it can be handled at the very end.
                            addKeyedRemoval(key);
                        } else {
                            // Only report the node as discarded if it is not keyed. We do this because
                            // at the end we loop through all keyed elements that were unmatched
                            // and then discard them in one final pass.
                            onNodeDiscarded(curChild);
                            if (curChild.firstChild) {
                                walkDiscardedChildNodes(curChild, skipKeyedNodes);
                            }
                        }

                        curChild = curChild.nextSibling;
                    }
                }
            }

            /**
             * Removes a DOM node out of the original DOM
             *
             * @param  {Node} node The node to remove
             * @param  {Node} parentNode The nodes parent
             * @param  {Boolean} skipKeyedNodes If true then elements with keys will be skipped and not discarded.
             * @return {undefined}
             */
            function removeNode(node, parentNode, skipKeyedNodes) {
                if (onBeforeNodeDiscarded(node) === false) {
                    return;
                }

                if (parentNode) {
                    parentNode.removeChild(node);
                }

                onNodeDiscarded(node);
                walkDiscardedChildNodes(node, skipKeyedNodes);
            }

            // // TreeWalker implementation is no faster, but keeping this around in case this changes in the future
            // function indexTree(root) {
            //     var treeWalker = document.createTreeWalker(
            //         root,
            //         NodeFilter.SHOW_ELEMENT);
            //
            //     var el;
            //     while((el = treeWalker.nextNode())) {
            //         var key = getNodeKey(el);
            //         if (key) {
            //             fromNodesLookup[key] = el;
            //         }
            //     }
            // }

            // // NodeIterator implementation is no faster, but keeping this around in case this changes in the future
            //
            // function indexTree(node) {
            //     var nodeIterator = document.createNodeIterator(node, NodeFilter.SHOW_ELEMENT);
            //     var el;
            //     while((el = nodeIterator.nextNode())) {
            //         var key = getNodeKey(el);
            //         if (key) {
            //             fromNodesLookup[key] = el;
            //         }
            //     }
            // }

            function indexTree(node) {
                if (node.nodeType === ELEMENT_NODE || node.nodeType === DOCUMENT_FRAGMENT_NODE$1) {
                    var curChild = node.firstChild;
                    while (curChild) {
                        var key = getNodeKey(curChild);
                        if (key) {
                            fromNodesLookup[key] = curChild;
                        }

                        // Walk recursively
                        indexTree(curChild);

                        curChild = curChild.nextSibling;
                    }
                }
            }

            indexTree(fromNode);

            function handleNodeAdded(el) {
                onNodeAdded(el);

                var curChild = el.firstChild;
                while (curChild) {
                    var nextSibling = curChild.nextSibling;

                    var key = getNodeKey(curChild);
                    if (key) {
                        var unmatchedFromEl = fromNodesLookup[key];
                        if (unmatchedFromEl && compareNodeNames(curChild, unmatchedFromEl)) {
                            curChild.parentNode.replaceChild(unmatchedFromEl, curChild);
                            morphEl(unmatchedFromEl, curChild);
                        }
                    }

                    handleNodeAdded(curChild);
                    curChild = nextSibling;
                }
            }

            function cleanupFromEl(fromEl, curFromNodeChild, curFromNodeKey) {
                // We have processed all of the "to nodes". If curFromNodeChild is
                // non-null then we still have some from nodes left over that need
                // to be removed
                while (curFromNodeChild) {
                    var fromNextSibling = curFromNodeChild.nextSibling;
                    if ((curFromNodeKey = getNodeKey(curFromNodeChild))) {
                        // Since the node is keyed it might be matched up later so we defer
                        // the actual removal to later
                        addKeyedRemoval(curFromNodeKey);
                    } else {
                        // NOTE: we skip nested keyed nodes from being removed since there is
                        //       still a chance they will be matched up later
                        removeNode(curFromNodeChild, fromEl, true /* skip keyed nodes */);
                    }
                    curFromNodeChild = fromNextSibling;
                }
            }

            function morphEl(fromEl, toEl, childrenOnly) {
                var toElKey = getNodeKey(toEl);

                if (toElKey) {
                    // If an element with an ID is being morphed then it will be in the final
                    // DOM so clear it out of the saved elements collection
                    delete fromNodesLookup[toElKey];
                }

                if (!childrenOnly) {
                    // optional
                    if (onBeforeElUpdated(fromEl, toEl) === false) {
                        return;
                    }

                    // update attributes on original DOM element first
                    morphAttrs(fromEl, toEl);
                    // optional
                    onElUpdated(fromEl);

                    if (onBeforeElChildrenUpdated(fromEl, toEl) === false) {
                        return;
                    }
                }

                if (fromEl.nodeName !== 'TEXTAREA') {
                  morphChildren(fromEl, toEl);
                } else {
                  specialElHandlers.TEXTAREA(fromEl, toEl);
                }
            }

            function morphChildren(fromEl, toEl) {
                var curToNodeChild = toEl.firstChild;
                var curFromNodeChild = fromEl.firstChild;
                var curToNodeKey;
                var curFromNodeKey;

                var fromNextSibling;
                var toNextSibling;
                var matchingFromEl;

                // walk the children
                outer: while (curToNodeChild) {
                    toNextSibling = curToNodeChild.nextSibling;
                    curToNodeKey = getNodeKey(curToNodeChild);

                    // walk the fromNode children all the way through
                    while (curFromNodeChild) {
                        fromNextSibling = curFromNodeChild.nextSibling;

                        if (curToNodeChild.isSameNode && curToNodeChild.isSameNode(curFromNodeChild)) {
                            curToNodeChild = toNextSibling;
                            curFromNodeChild = fromNextSibling;
                            continue outer;
                        }

                        curFromNodeKey = getNodeKey(curFromNodeChild);

                        var curFromNodeType = curFromNodeChild.nodeType;

                        // this means if the curFromNodeChild doesnt have a match with the curToNodeChild
                        var isCompatible = undefined;

                        if (curFromNodeType === curToNodeChild.nodeType) {
                            if (curFromNodeType === ELEMENT_NODE) {
                                // Both nodes being compared are Element nodes

                                if (curToNodeKey) {
                                    // The target node has a key so we want to match it up with the correct element
                                    // in the original DOM tree
                                    if (curToNodeKey !== curFromNodeKey) {
                                        // The current element in the original DOM tree does not have a matching key so
                                        // let's check our lookup to see if there is a matching element in the original
                                        // DOM tree
                                        if ((matchingFromEl = fromNodesLookup[curToNodeKey])) {
                                            if (fromNextSibling === matchingFromEl) {
                                                // Special case for single element removals. To avoid removing the original
                                                // DOM node out of the tree (since that can break CSS transitions, etc.),
                                                // we will instead discard the current node and wait until the next
                                                // iteration to properly match up the keyed target element with its matching
                                                // element in the original tree
                                                isCompatible = false;
                                            } else {
                                                // We found a matching keyed element somewhere in the original DOM tree.
                                                // Let's move the original DOM node into the current position and morph
                                                // it.

                                                // NOTE: We use insertBefore instead of replaceChild because we want to go through
                                                // the `removeNode()` function for the node that is being discarded so that
                                                // all lifecycle hooks are correctly invoked
                                                fromEl.insertBefore(matchingFromEl, curFromNodeChild);

                                                // fromNextSibling = curFromNodeChild.nextSibling;

                                                if (curFromNodeKey) {
                                                    // Since the node is keyed it might be matched up later so we defer
                                                    // the actual removal to later
                                                    addKeyedRemoval(curFromNodeKey);
                                                } else {
                                                    // NOTE: we skip nested keyed nodes from being removed since there is
                                                    //       still a chance they will be matched up later
                                                    removeNode(curFromNodeChild, fromEl, true /* skip keyed nodes */);
                                                }

                                                curFromNodeChild = matchingFromEl;
                                            }
                                        } else {
                                            // The nodes are not compatible since the "to" node has a key and there
                                            // is no matching keyed node in the source tree
                                            isCompatible = false;
                                        }
                                    }
                                } else if (curFromNodeKey) {
                                    // The original has a key
                                    isCompatible = false;
                                }

                                isCompatible = isCompatible !== false && compareNodeNames(curFromNodeChild, curToNodeChild);
                                if (isCompatible) {
                                    // We found compatible DOM elements so transform
                                    // the current "from" node to match the current
                                    // target DOM node.
                                    // MORPH
                                    morphEl(curFromNodeChild, curToNodeChild);
                                }

                            } else if (curFromNodeType === TEXT_NODE || curFromNodeType == COMMENT_NODE) {
                                // Both nodes being compared are Text or Comment nodes
                                isCompatible = true;
                                // Simply update nodeValue on the original node to
                                // change the text value
                                if (curFromNodeChild.nodeValue !== curToNodeChild.nodeValue) {
                                    curFromNodeChild.nodeValue = curToNodeChild.nodeValue;
                                }

                            }
                        }

                        if (isCompatible) {
                            // Advance both the "to" child and the "from" child since we found a match
                            // Nothing else to do as we already recursively called morphChildren above
                            curToNodeChild = toNextSibling;
                            curFromNodeChild = fromNextSibling;
                            continue outer;
                        }

                        // No compatible match so remove the old node from the DOM and continue trying to find a
                        // match in the original DOM. However, we only do this if the from node is not keyed
                        // since it is possible that a keyed node might match up with a node somewhere else in the
                        // target tree and we don't want to discard it just yet since it still might find a
                        // home in the final DOM tree. After everything is done we will remove any keyed nodes
                        // that didn't find a home
                        if (curFromNodeKey) {
                            // Since the node is keyed it might be matched up later so we defer
                            // the actual removal to later
                            addKeyedRemoval(curFromNodeKey);
                        } else {
                            // NOTE: we skip nested keyed nodes from being removed since there is
                            //       still a chance they will be matched up later
                            removeNode(curFromNodeChild, fromEl, true /* skip keyed nodes */);
                        }

                        curFromNodeChild = fromNextSibling;
                    } // END: while(curFromNodeChild) {}

                    // If we got this far then we did not find a candidate match for
                    // our "to node" and we exhausted all of the children "from"
                    // nodes. Therefore, we will just append the current "to" node
                    // to the end
                    if (curToNodeKey && (matchingFromEl = fromNodesLookup[curToNodeKey]) && compareNodeNames(matchingFromEl, curToNodeChild)) {
                        fromEl.appendChild(matchingFromEl);
                        // MORPH
                        morphEl(matchingFromEl, curToNodeChild);
                    } else {
                        var onBeforeNodeAddedResult = onBeforeNodeAdded(curToNodeChild);
                        if (onBeforeNodeAddedResult !== false) {
                            if (onBeforeNodeAddedResult) {
                                curToNodeChild = onBeforeNodeAddedResult;
                            }

                            if (curToNodeChild.actualize) {
                                curToNodeChild = curToNodeChild.actualize(fromEl.ownerDocument || doc);
                            }
                            fromEl.appendChild(curToNodeChild);
                            handleNodeAdded(curToNodeChild);
                        }
                    }

                    curToNodeChild = toNextSibling;
                    curFromNodeChild = fromNextSibling;
                }

                cleanupFromEl(fromEl, curFromNodeChild, curFromNodeKey);

                var specialElHandler = specialElHandlers[fromEl.nodeName];
                if (specialElHandler) {
                    specialElHandler(fromEl, toEl);
                }
            } // END: morphChildren(...)

            var morphedNode = fromNode;
            var morphedNodeType = morphedNode.nodeType;
            var toNodeType = toNode.nodeType;

            if (!childrenOnly) {
                // Handle the case where we are given two DOM nodes that are not
                // compatible (e.g. <div> --> <span> or <div> --> TEXT)
                if (morphedNodeType === ELEMENT_NODE) {
                    if (toNodeType === ELEMENT_NODE) {
                        if (!compareNodeNames(fromNode, toNode)) {
                            onNodeDiscarded(fromNode);
                            morphedNode = moveChildren(fromNode, createElementNS(toNode.nodeName, toNode.namespaceURI));
                        }
                    } else {
                        // Going from an element node to a text node
                        morphedNode = toNode;
                    }
                } else if (morphedNodeType === TEXT_NODE || morphedNodeType === COMMENT_NODE) { // Text or comment node
                    if (toNodeType === morphedNodeType) {
                        if (morphedNode.nodeValue !== toNode.nodeValue) {
                            morphedNode.nodeValue = toNode.nodeValue;
                        }

                        return morphedNode;
                    } else {
                        // Text node to something else
                        morphedNode = toNode;
                    }
                }
            }

            if (morphedNode === toNode) {
                // The "to node" was not compatible with the "from node" so we had to
                // toss out the "from node" and use the "to node"
                onNodeDiscarded(fromNode);
            } else {
                if (toNode.isSameNode && toNode.isSameNode(morphedNode)) {
                    return;
                }

                morphEl(morphedNode, toNode, childrenOnly);

                // We now need to loop over any keyed nodes that might need to be
                // removed. We only do the removal if we know that the keyed node
                // never found a match. When a keyed node is matched up we remove
                // it out of fromNodesLookup and we use fromNodesLookup to determine
                // if a keyed node has been matched up or not
                if (keyedRemovalList) {
                    for (var i=0, len=keyedRemovalList.length; i<len; i++) {
                        var elToRemove = fromNodesLookup[keyedRemovalList[i]];
                        if (elToRemove) {
                            removeNode(elToRemove, elToRemove.parentNode, false);
                        }
                    }
                }
            }

            if (!childrenOnly && morphedNode !== fromNode && fromNode.parentNode) {
                if (morphedNode.actualize) {
                    morphedNode = morphedNode.actualize(fromNode.ownerDocument || doc);
                }
                // If we had to swap out the from node with a new node because the old
                // node was not compatible with the target node then we need to
                // replace the old DOM node in the original DOM tree. This is only
                // possible if the original DOM node was part of a DOM tree which
                // we know is the case if it has a parent node.
                fromNode.parentNode.replaceChild(morphedNode, fromNode);
            }

            return morphedNode;
        };
    }

    var morphdom = morphdomFactory(morphAttrs);

    return morphdom;

}));