react diff patch

diff.js

export default function diff (parentNode, prevNodeMap, newNodeMap) {
  let lastIndex = 0
  let lastRightNode = null
  let patch = []
  let mountIndex = 0
  for (let name in newNodeMap) {
    if (newNodeMap.hasOwnProperty(name)) {
      let newNode = newNodeMap[name]
      let prevNode = prevNodeMap[name]
      if (prevNode) {
        let prevIndex = prevNode.index
        if (prevIndex > lastIndex) {
          lastIndex = prevIndex
        } else {
          patch.push({
            type: 'move',
            node: prevNode,
            insertNode: lastRightNode
          })
        }
        lastRightNode = prevNode
        prevNode.index = mountIndex++
      } else {
        patch.push({
          type: 'insert',
          node: newNode,
          insertNode: lastRightNode
        })
        newNode.index = mountIndex++
        lastRightNode = newNode
      }
    }
  }
  for (let name in prevNodeMap) {
    if (prevNodeMap.hasOwnProperty(name) && !newNodeMap.hasOwnProperty(name)) {
      let prevNode = prevNodeMap[name]
      patch.push({
        type: 'remove',
        node: prevNode
      })
    }
  }
  function getNodeAfter (parentNode, node) {
    return node ? node.nextSibling : parentNode.firstChild
  }

  patch.forEach(action => {
    switch (action.type) {
      case 'move':
        parentNode.insertBefore(action.node, getNodeAfter(parentNode, action.insertNode))
        break
      case 'insert':
        parentNode.insertBefore(action.node, getNodeAfter(parentNode, action.insertNode))
        break
      case 'remove':
        parentNode.removeChild(action.node)
    }
  })
}