var element = {
      tagName: 'div',
      props: {
        class: 'box'
      },
      children: {
        {
          tagName: 'p',
          props: {
            class: 'p1'
          },
          children: ['我是p1']
        }, 
         {
          tagName: 'p',
          props: {
            class: 'p2'
          },
          children: ['我是p2']
        }, 
        {
          tagName: 'p',
          props: {
            class: 'p3'
          },
          children: ['我是p3']
        },
      }
    }

function Element(tagName, props, children) {
    this.tagName = tagName
    this.props = props
    this.children = children
}

Element.prototype.render = function () {
    const { tagName, props, children } = this
    var el = document.createElement(tagName)
    for (key in props) {
        el.setAttribute(key, props[key])
    }
    children.forEach((item) => {
        const childEl = (item instanceof Element) ?
              item.render() :
        document.createTextNode(item)
        el.appendChild(childEl)
    })
    return el
}

let virtualDom = new Element('div', { class: 'box' }, [
    new Element('p', { class: 'p1' }, ['我是p1']),
    new Element('p', { class: 'p2' }, ['我是p2']),
    new Element('p', { class: 'p3' }, ['我是p3']),
])

let a = virtualDom.render()
document.body.appendChild(a)

// diff 函數(shù)，對比兩棵樹
function diff(oldTree, newTree) {
    var patchs = {};  // 偽數(shù)組，記錄差異
    //  對4種節(jié)點(diǎn)做錯判斷
    dfWork(oldTree, newTree, patchs, index)

    return patchs

}
function dfWork(oldTree, newTree, patchs, index) {
    let currentPatch = []

    if (1) { // 對節(jié)點(diǎn)的刪除
        currentPatch.push()
    } else if (3) { // 對節(jié)點(diǎn)的文本的更換
        currentPatch.push()

    } else { // 修改節(jié)點(diǎn)的props 對children的檢查
        // 對props作diff算法，把變化記錄到patchs中。
        currentPatch.push({ type: patch.PROPS, props: propsPatches })
        // 然后需要對子節(jié)點(diǎn)作diff算法
        diffChildren(oldNode.children, newNode.children, index, patches, currentPatch)
    }
}
function diffChildren(oldChildren, newChildren, index, patches, currentPatch) {

    // 對子節(jié)點(diǎn)作diff算法，遍歷子節(jié)點(diǎn)，遞歸調(diào)用dfWork，做差異得到patchs

}
// 把變化應(yīng)用在真實的DOM樹上
function patch(node, patchs) {
    // node為老的DOM樹，patchs變化。
    // 我們會遍歷這個patchs，并且把node和patch對應(yīng)上，
}
function applyPatch(node, patchs) {
    // 應(yīng)為每個節(jié)點(diǎn)可能有多個變化，所以也需要遍歷
    switch (patchs.type) {
        case REPLACE: // 節(jié)點(diǎn)替換
            // node.render() 
            break;
        case REORDER:  // 節(jié)點(diǎn)的移動刪除新增子節(jié)點(diǎn)。

            break;
        case PROPS:
            // setProps
            break;
        case TEXT: // 對節(jié)點(diǎn)文本的修改
            // node.nodeValue
            break;

        default:
            break;
    }
}