源码大概4600-5600行

function initRender (vm) {
  vm._vnode = null; // the root of the child tree
  vm._staticTrees = null; // v-once cached trees
  // 获取options
  var options = vm.$options;
  var parentVnode = vm.$vnode = options._parentVnode; // the placeholder node in parent tree
  var renderContext = parentVnode && parentVnode.context;
  //解析slot对象
  vm.$slots = resolveSlots(options._renderChildren, renderContext);
  vm.$scopedSlots = emptyObject;
  // bind the createElement fn to this instance
  // so that we get proper render context inside it.
  // args order: tag, data, children, normalizationType, alwaysNormalize
  // internal version is used by render functions compiled from templates
  vm._c = function (a, b, c, d) { return createElement(vm, a, b, c, d, false); };
  // normalization is always applied for the public version, used in
  // user-written render functions.
  vm.$createElement = function (a, b, c, d) { return createElement(vm, a, b, c, d, true); };

  // $attrs & $listeners are exposed for easier HOC creation.
  // they need to be reactive so that HOCs using them are always updated
  var parentData = parentVnode && parentVnode.data;

  /* istanbul ignore else */
  //监听data属性变化
  {
    defineReactive(vm, '$attrs', parentData && parentData.attrs || emptyObject, function () {
      !isUpdatingChildComponent && warn("$attrs is readonly.", vm);
    }, true);
    defineReactive(vm, '$listeners', options._parentListeners || emptyObject, function () {
      !isUpdatingChildComponent && warn("$listeners is readonly.", vm);
    }, true);
  }
}
// 生成vnode对象来实现记录虚拟dom树上的属性
function renderMixin (Vue) {
  // install runtime convenience helpers
  installRenderHelpers(Vue.prototype);

  Vue.prototype.$nextTick = function (fn) {
    return nextTick(fn, this)
  };

  Vue.prototype._render = function () {
    var vm = this;
    var ref = vm.$options;
    var render = ref.render;
    var _parentVnode = ref._parentVnode;

    // reset _rendered flag on slots for duplicate slot check
    {
      for (var key in vm.$slots) {
        // $flow-disable-line
        vm.$slots[key]._rendered = false;
      }
    }

    if (_parentVnode) {
      vm.$scopedSlots = _parentVnode.data.scopedSlots || emptyObject;
    }

    // set parent vnode. this allows render functions to have access
    // to the data on the placeholder node.
    vm.$vnode = _parentVnode;
    // render self
    var vnode;
    try {
      vnode = render.call(vm._renderProxy, vm.$createElement);
    } catch (e) {
      handleError(e, vm, "render");
      // return error render result,
      // or previous vnode to prevent render error causing blank component
      /* istanbul ignore else */
      {
        if (vm.$options.renderError) {
          try {
            vnode = vm.$options.renderError.call(vm._renderProxy, vm.$createElement, e);
          } catch (e) {
            handleError(e, vm, "renderError");
            vnode = vm._vnode;
          }
        } else {
          vnode = vm._vnode;
        }
      }
    }
    // return empty vnode in case the render function errored out
    if (!(vnode instanceof VNode)) {
      if ("development" !== 'production' && Array.isArray(vnode)) {
        warn(
          'Multiple root nodes returned from render function. Render function ' +
          'should return a single root node.',
          vm
        );
      }
      vnode = createEmptyVNode();
    }
    // set parent
    vnode.parent = _parentVnode;
    return vnode
  };
}

/*  */

var uid$3 = 0;

function initMixin (Vue) {
  Vue.prototype._init = function (options) {
    var vm = this;
    // a uid
    vm._uid = uid$3++;

    var startTag, endTag;
    /* istanbul ignore if */
    if ("development" !== 'production' && config.performance && mark) {
      startTag = "vue-perf-start:" + (vm._uid);
      endTag = "vue-perf-end:" + (vm._uid);
      mark(startTag);
    }

    // a flag to avoid this being observed
    vm._isVue = true;
    // merge options
    // 处理options
    if (options && options._isComponent) {
      // optimize internal component instantiation
      // since dynamic options merging is pretty slow, and none of the
      // internal component options needs special treatment.
      initInternalComponent(vm, options);
    } else {
      vm.$options = mergeOptions(
        resolveConstructorOptions(vm.constructor),
        options || {},
        vm
      );
    }
    // 支持proxy,调用render函数
    /* istanbul ignore else */
    {
      initProxy(vm);
    }
    // expose real self

    vm._self = vm;
    // 初始化生命周期函数
    initLifecycle(vm);
    // 初始化事件
    initEvents(vm);
    // 初始化vNode对象，设置监听
    initRender(vm);
    //执行beforeCreate周期
    callHook(vm, 'beforeCreate');
    // 处理注入，设置监听
    initInjections(vm); // resolve injections before data/props
    initState(vm);
    // 处理provice
    initProvide(vm); // resolve provide after data/props
    // 调用生命周期created
    callHook(vm, 'created');

    /* istanbul ignore if */
    // 设置perfomance监听，那就测试组件和开始标签和结束标签渲染的时间和性能
    if ("development" !== 'production' && config.performance && mark) {
      vm._name = formatComponentName(vm, false);
      mark(endTag);
      measure(("vue " + (vm._name) + " init"), startTag, endTag);
    }

    if (vm.$options.el) {
      vm.$mount(vm.$options.el);
    }
  };
}
// 处理组件options
function initInternalComponent (vm, options) {
  // 构造函数的options
  var opts = vm.$options = Object.create(vm.constructor.options);
  // doing this because it's faster than dynamic enumeration.
  // 父组件Vnode
  var parentVnode = options._parentVnode;
  // 构造函数options设置parent,_parentVnode,_parentElm,_refElm参数
  opts.parent = options.parent;
  opts._parentVnode = parentVnode;
  opts._parentElm = options._parentElm;
  opts._refElm = options._refElm;
  // 设置父组件的options
  var vnodeComponentOptions = parentVnode.componentOptions;
  // 设置构造函数options中propsData,_parentListeners,_renderChildren,_componentTag
  opts.propsData = vnodeComponentOptions.propsData;
  opts._parentListeners = vnodeComponentOptions.listeners;
  opts._renderChildren = vnodeComponentOptions.children;
  opts._componentTag = vnodeComponentOptions.tag;
  // 如果options中有render
  if (options.render) {
    opts.render = options.render;
    opts.staticRenderFns = options.staticRenderFns;
  }
}
// 处理构造函数的options
function resolveConstructorOptions (Ctor) {
  // 够着函数的options
  var options = Ctor.options;
  //如果仍然有上一级的构造函数，
  if (Ctor.super) {
    //获取上一级构造函数的options
    var superOptions = resolveConstructorOptions(Ctor.super);
    //获取构造函数的缓存superOptions
    var cachedSuperOptions = Ctor.superOptions;
    // 获取上一级构造函数的options和构造函数的缓存superOptions不同
    if (superOptions !== cachedSuperOptions) {
      // super option changed,
      // need to resolve new options.
      // 将构造函数的superOptions设置为取到的构造函数superOptions
      Ctor.superOptions = superOptions;
      // check if there are any late-modified/attached options (#4976)
      var modifiedOptions = resolveModifiedOptions(Ctor);
      // update base extend options
      if (modifiedOptions) {
        extend(Ctor.extendOptions, modifiedOptions);
      }
      options = Ctor.options = mergeOptions(superOptions, Ctor.extendOptions);
      if (options.name) {
        options.components[options.name] = Ctor;
      }
    }
  }
  return options
}
function resolveModifiedOptions (Ctor) {
  var modified;
  var latest = Ctor.options;
  var extended = Ctor.extendOptions;
  var sealed = Ctor.sealedOptions;
  for (var key in latest) {
    if (latest[key] !== sealed[key]) {
      if (!modified) { modified = {}; }
      modified[key] = dedupe(latest[key], extended[key], sealed[key]);
    }
  }
  return modified
}

// 选择中最新的options中extendOptions中有或者sealedOptions中没有的options
function dedupe (latest, extended, sealed) {
  // compare latest and sealed to ensure lifecycle hooks won't be duplicated
  // between merges
  if (Array.isArray(latest)) {
    var res = [];
    sealed = Array.isArray(sealed) ? sealed : [sealed];
    extended = Array.isArray(extended) ? extended : [extended];
    for (var i = 0; i < latest.length; i++) {
      // push original options and not sealed options to exclude duplicated options
      if (extended.indexOf(latest[i]) >= 0 || sealed.indexOf(latest[i]) < 0) {
        res.push(latest[i]);
      }
    }
    return res
  } else {
    return latest
  }
}
// vue的构造函数
function Vue (options) {
  if ("development" !== 'production' &&
    !(this instanceof Vue)
  ) {
    warn('Vue is a constructor and should be called with the `new` keyword');
  }
  // 各种，初始化调用$mouted
  this._init(options);
}
//组件初始化
initMixin(Vue);
// 监听
stateMixin(Vue);
// 给vue原型链上事件绑定一些方法和手机events集合
eventsMixin(Vue);
// 生命周期绑定方法
lifecycleMixin(Vue);
// 解析
renderMixin(Vue);

/*  */
// 调用插件
function initUse (Vue) {
  Vue.use = function (plugin) {
    var installedPlugins = (this._installedPlugins || (this._installedPlugins = []));
    if (installedPlugins.indexOf(plugin) > -1) {
      return this
    }

    // additional parameters
    var args = toArray(arguments, 1);
    args.unshift(this);
    if (typeof plugin.install === 'function') {
      plugin.install.apply(plugin, args);
    } else if (typeof plugin === 'function') {
      plugin.apply(null, args);
    }
    installedPlugins.push(plugin);
    return this
  };
}

/*  */

function initMixin$1 (Vue) {
  Vue.mixin = function (mixin) {
    this.options = mergeOptions(this.options, mixin);
    return this
  };
}

/*  */
// vue扩展函数
function initExtend (Vue) {
  /**
   * Each instance constructor, including Vue, has a unique
   * cid. This enables us to create wrapped "child
   * constructors" for prototypal inheritance and cache them.
   */
  Vue.cid = 0;
  var cid = 1;

  /**
   * Class inheritance
   */
  // 扩展
  Vue.extend = function (extendOptions) {
    extendOptions = extendOptions || {};
    var Super = this;
    var SuperId = Super.cid;
    var cachedCtors = extendOptions._Ctor || (extendOptions._Ctor = {});
    if (cachedCtors[SuperId]) {
      return cachedCtors[SuperId]
    }

    var name = extendOptions.name || Super.options.name;
    if ("development" !== 'production' && name) {
      validateComponentName(name);
    }

    var Sub = function VueComponent (options) {
      this._init(options);
    };
    Sub.prototype = Object.create(Super.prototype);
    Sub.prototype.constructor = Sub;
    Sub.cid = cid++;
    Sub.options = mergeOptions(
      Super.options,
      extendOptions
    );
    Sub['super'] = Super;

    // For props and computed properties, we define the proxy getters on
    // the Vue instances at extension time, on the extended prototype. This
    // avoids Object.defineProperty calls for each instance created.
    if (Sub.options.props) {
      initProps$1(Sub);
    }
    if (Sub.options.computed) {
      initComputed$1(Sub);
    }

    // allow further extension/mixin/plugin usage
    Sub.extend = Super.extend;
    Sub.mixin = Super.mixin;
    Sub.use = Super.use;

    // create asset registers, so extended classes
    // can have their private assets too.
    ASSET_TYPES.forEach(function (type) {
      Sub[type] = Super[type];
    });
    // enable recursive self-lookup
    if (name) {
      Sub.options.components[name] = Sub;
    }

    // keep a reference to the super options at extension time.
    // later at instantiation we can check if Super's options have
    // been updated.
    Sub.superOptions = Super.options;
    Sub.extendOptions = extendOptions;
    Sub.sealedOptions = extend({}, Sub.options);

    // cache constructor
    cachedCtors[SuperId] = Sub;
    return Sub
  };
}

function initProps$1 (Comp) {
  var props = Comp.options.props;
  for (var key in props) {
    proxy(Comp.prototype, "_props", key);
  }
}

function initComputed$1 (Comp) {
  var computed = Comp.options.computed;
  for (var key in computed) {
    defineComputed(Comp.prototype, key, computed[key]);
  }
}

/*  */
// 创建vue的几个属性方法，component，direactive
function initAssetRegisters (Vue) {
  /**
   * Create asset registration methods.
   */
  ASSET_TYPES.forEach(function (type) {
    Vue[type] = function (
      id,
      definition
    ) {
      if (!definition) {
        return this.options[type + 's'][id]
      } else {
        /* istanbul ignore if */
        if ("development" !== 'production' && type === 'component') {
          validateComponentName(id);
        }
        if (type === 'component' && isPlainObject(definition)) {
          definition.name = definition.name || id;
          definition = this.options._base.extend(definition);
        }
        if (type === 'directive' && typeof definition === 'function') {
          definition = { bind: definition, update: definition };
        }
        this.options[type + 's'][id] = definition;
        
        return definition
      }
    };
  });
}

/*  */

function getComponentName (opts) {
  return opts && (opts.Ctor.options.name || opts.tag)
}
// pattern分三种格式，数组包含，字符串包含，正则匹配
function matches (pattern, name) {
  if (Array.isArray(pattern)) {
    return pattern.indexOf(name) > -1
  } else if (typeof pattern === 'string') {
    return pattern.split(',').indexOf(name) > -1
  } else if (isRegExp(pattern)) {
    return pattern.test(name)
  }
  /* istanbul ignore next */
  return false
}

function pruneCache (keepAliveInstance, filter) {
  var cache = keepAliveInstance.cache;
  var keys = keepAliveInstance.keys;
  var _vnode = keepAliveInstance._vnode;
  for (var key in cache) {
    var cachedNode = cache[key];
    if (cachedNode) {
      var name = getComponentName(cachedNode.componentOptions);
      if (name && !filter(name)) {
        pruneCacheEntry(cache, key, keys, _vnode);
      }
    }
  }
}

function pruneCacheEntry (
  cache,
  key,
  keys,
  current
) {
  var cached$$1 = cache[key];
  // 缓存的tag不能与当前的tag,组件销毁，属性删除
  if (cached$$1 && (!current || cached$$1.tag !== current.tag)) {
    cached$$1.componentInstance.$destroy();
  }
  cache[key] = null;
  remove(keys, key);
}

var patternTypes = [String, RegExp, Array];
// 定义keppalived的属性和方法等
var KeepAlive = {
  name: 'keep-alive',
  abstract: true,

  props: {
    include: patternTypes,
    exclude: patternTypes,
    max: [String, Number]
  },

  created: function created () {
    this.cache = Object.create(null);
    this.keys = [];
  },

  destroyed: function destroyed () {
    var this$1 = this;

    for (var key in this$1.cache) {
      pruneCacheEntry(this$1.cache, key, this$1.keys);
    }
  },

  mounted: function mounted () {
    var this$1 = this;

    this.$watch('include', function (val) {
      pruneCache(this$1, function (name) { return matches(val, name); });
    });
    this.$watch('exclude', function (val) {
      pruneCache(this$1, function (name) { return !matches(val, name); });
    });
  },

  render: function render () {
    var slot = this.$slots.default;
    var vnode = getFirstComponentChild(slot);
    var componentOptions = vnode && vnode.componentOptions;
    if (componentOptions) {
      // check pattern
      var name = getComponentName(componentOptions);
      var ref = this;
      var include = ref.include;
      var exclude = ref.exclude;
      if (
        // not included
        (include && (!name || !matches(include, name))) ||
        // excluded
        (exclude && name && matches(exclude, name))
      ) {
        return vnode
      }

      var ref$1 = this;
      var cache = ref$1.cache;
      var keys = ref$1.keys;
      var key = vnode.key == null
        // same constructor may get registered as different local components
        // so cid alone is not enough (#3269)
        ? componentOptions.Ctor.cid + (componentOptions.tag ? ("::" + (componentOptions.tag)) : '')
        : vnode.key;
      if (cache[key]) {
        vnode.componentInstance = cache[key].componentInstance;
        // make current key freshest
        remove(keys, key);
        keys.push(key);
      } else {
        cache[key] = vnode;
        keys.push(key);
        // prune oldest entry
        if (this.max && keys.length > parseInt(this.max)) {
          pruneCacheEntry(cache, keys[0], keys, this._vnode);
        }
      }

      vnode.data.keepAlive = true;
    }
    return vnode || (slot && slot[0])
  }
}

var builtInComponents = {
  KeepAlive: KeepAlive
}

/*  */
// 初始化vue全局的方法
function initGlobalAPI (Vue) {
  // config
  var configDef = {};
  configDef.get = function () { return config; };
  {
    configDef.set = function () {
      warn(
        'Do not replace the Vue.config object, set individual fields instead.'
      );
    };
  }
  Object.defineProperty(Vue, 'config', configDef);

  // exposed util methods.
  // NOTE: these are not considered part of the public API - avoid relying on
  // them unless you are aware of the risk.
  Vue.util = {
    warn: warn,
    extend: extend,
    mergeOptions: mergeOptions,
    defineReactive: defineReactive
  };

  Vue.set = set;
  Vue.delete = del;
  Vue.nextTick = nextTick;

  Vue.options = Object.create(null);
  ASSET_TYPES.forEach(function (type) {
    Vue.options[type + 's'] = Object.create(null);
  });

  // this is used to identify the "base" constructor to extend all plain-object
  // components with in Weex's multi-instance scenarios.
  Vue.options._base = Vue;

  extend(Vue.options.components, builtInComponents);

  initUse(Vue);
  initMixin$1(Vue);
  initExtend(Vue);
  initAssetRegisters(Vue);
}

initGlobalAPI(Vue);
// 是否是运行在服务器
Object.defineProperty(Vue.prototype, '$isServer', {
  get: isServerRendering
});

Object.defineProperty(Vue.prototype, '$ssrContext', {
  get: function get () {
    /* istanbul ignore next */
    return this.$vnode && this.$vnode.ssrContext
  }
});

// 为服务器渲染暴露接口
// expose FunctionalRenderContext for ssr runtime helper installation
Object.defineProperty(Vue, 'FunctionalRenderContext', {
  value: FunctionalRenderContext
});

Vue.version = '2.5.17';

/*  */

// these are reserved for web because they are directly compiled away
// during template compilation
// 是否是style,class保留属性
var isReservedAttr = makeMap('style,class');

// attributes that should be using props for binding
// 必须用props绑定的input 类型
var acceptValue = makeMap('input,textarea,option,select,progress');
var mustUseProp = function (tag, type, attr) {
  return (
    (attr === 'value' && acceptValue(tag)) && type !== 'button' ||
    (attr === 'selected' && tag === 'option') ||
    (attr === 'checked' && tag === 'input') ||
    (attr === 'muted' && tag === 'video')
  )
};

var isEnumeratedAttr = makeMap('contenteditable,draggable,spellcheck');

var isBooleanAttr = makeMap(
  'allowfullscreen,async,autofocus,autoplay,checked,compact,controls,declare,' +
  'default,defaultchecked,defaultmuted,defaultselected,defer,disabled,' +
  'enabled,formnovalidate,hidden,indeterminate,inert,ismap,itemscope,loop,multiple,' +
  'muted,nohref,noresize,noshade,novalidate,nowrap,open,pauseonexit,readonly,' +
  'required,reversed,scoped,seamless,selected,sortable,translate,' +
  'truespeed,typemustmatch,visible'
);

var xlinkNS = 'http://www.w3.org/1999/xlink';
// 使用xlink
var isXlink = function (name) {
  return name.charAt(5) === ':' && name.slice(0, 5) === 'xlink'
};

var getXlinkProp = function (name) {
  return isXlink(name) ? name.slice(6, name.length) : ''
};
// 是否是合法的属性
var isFalsyAttrValue = function (val) {
  return val == null || val === false
};

/*  */

function genClassForVnode (vnode) {
  var data = vnode.data;
  var parentNode = vnode;
  var childNode = vnode;
  // 合并子组件的类
  while (isDef(childNode.componentInstance)) {
    childNode = childNode.componentInstance._vnode;
    if (childNode && childNode.data) {
      data = mergeClassData(childNode.data, data);
    }
  }
  // 合并父组件的类
  while (isDef(parentNode = parentNode.parent)) {
    if (parentNode && parentNode.data) {
      data = mergeClassData(data, parentNode.data);
    }
  }
  return renderClass(data.staticClass, data.class)
}
// 合并class
function mergeClassData (child, parent) {
  return {
    staticClass: concat(child.staticClass, parent.staticClass),
    class: isDef(child.class)
      ? [child.class, parent.class]
      : parent.class
  }
}
// 合并类成字符串并返回
function renderClass (
  staticClass,
  dynamicClass
) {
  if (isDef(staticClass) || isDef(dynamicClass)) {
    return concat(staticClass, stringifyClass(dynamicClass))
  }
  /* istanbul ignore next */
  return ''
}
// 合并参数
function concat (a, b) {
  return a ? b ? (a + ' ' + b) : a : (b || '')
}

function stringifyClass (value) {
  if (Array.isArray(value)) {
    return stringifyArray(value)
  }
  if (isObject(value)) {
    return stringifyObject(value)
  }
  if (typeof value === 'string') {
    return value
  }
  /* istanbul ignore next */
  return ''
}
// 合并数组的类
function stringifyArray (value) {
  var res = '';
  var stringified;
  for (var i = 0, l = value.length; i < l; i++) {
    if (isDef(stringified = stringifyClass(value[i])) && stringified !== '') {
      if (res) { res += ' '; }
      res += stringified;
    }
  }
  return res
}
// 合并对象的类
function stringifyObject (value) {
  var res = '';
  for (var key in value) {
    if (value[key]) {
      if (res) { res += ' '; }
      res += key;
    }
  }
  return res
}

/*  */

var namespaceMap = {
  svg: 'http://www.w3.org/2000/svg',
  math: 'http://www.w3.org/1998/Math/MathML'
};
// html 标签的集合
var isHTMLTag = makeMap(
  'html,body,base,head,link,meta,style,title,' +
  'address,article,aside,footer,header,h1,h2,h3,h4,h5,h6,hgroup,nav,section,' +
  'div,dd,dl,dt,figcaption,figure,picture,hr,img,li,main,ol,p,pre,ul,' +
  'a,b,abbr,bdi,bdo,br,cite,code,data,dfn,em,i,kbd,mark,q,rp,rt,rtc,ruby,' +
  's,samp,small,span,strong,sub,sup,time,u,var,wbr,area,audio,map,track,video,' +
  'embed,object,param,source,canvas,script,noscript,del,ins,' +
  'caption,col,colgroup,table,thead,tbody,td,th,tr,' +
  'button,datalist,fieldset,form,input,label,legend,meter,optgroup,option,' +
  'output,progress,select,textarea,' +
  'details,dialog,menu,menuitem,summary,' +
  'content,element,shadow,template,blockquote,iframe,tfoot'
);

// this map is intentionally selective, only covering SVG elements that may
// contain child elements.
// svg的集合
var isSVG = makeMap(
  'svg,animate,circle,clippath,cursor,defs,desc,ellipse,filter,font-face,' +
  'foreignObject,g,glyph,image,line,marker,mask,missing-glyph,path,pattern,' +
  'polygon,polyline,rect,switch,symbol,text,textpath,tspan,use,view',
  true
);
// 是否是pre标签
var isPreTag = function (tag) { return tag === 'pre'; };
// 是否是html标签或者svg标签，这些是要保留的标签
var isReservedTag = function (tag) {
  return isHTMLTag(tag) || isSVG(tag)
};
// 命名空间 svg或者math
function getTagNamespace (tag) {
  if (isSVG(tag)) {
    return 'svg'
  }
  // basic support for MathML
  // note it doesn't support other MathML elements being component roots
  if (tag === 'math') {
    return 'math'
  }
}
// 定义对象,用来保存未知标签
var unknownElementCache = Object.create(null);
// 判断是否是未知标签
function isUnknownElement (tag) {
  /* istanbul ignore if */
  //如果不是浏览器环境，return true
  if (!inBrowser) {
    return true
  }
  // 如果是html的tag,或者svg，返回false
  if (isReservedTag(tag)) {
    return false
  }
  tag = tag.toLowerCase();
  /* istanbul ignore if */
  // 如果未知标签对象有缓存，返回其保存的结果
  if (unknownElementCache[tag] != null) {
    return unknownElementCache[tag]
  }
  var el = document.createElement(tag);
  // tag里有中线就用构造函数去判断否者用正则去校验
  if (tag.indexOf('-') > -1) {
    // http://stackoverflow.com/a/28210364/1070244
    return (unknownElementCache[tag] = (
      el.constructor === window.HTMLUnknownElement ||
      el.constructor === window.HTMLElement
    ))
  } else {
    return (unknownElementCache[tag] = /HTMLUnknownElement/.test(el.toString()))
  }
}
// input type的类型集合
var isTextInputType = makeMap('text,number,password,search,email,tel,url');

/*  */

/**
 * Query an element selector if it's not an element already.
 */
// 获取dom
function query (el) {
  if (typeof el === 'string') {
    var selected = document.querySelector(el);
    if (!selected) {
      "development" !== 'production' && warn(
        'Cannot find element: ' + el
      );
      return document.createElement('div')
    }
    return selected
  } else {
    return el
  }
}

/*  */
// 创建dom,如果是select，判断vnode里的multiple属性判断select是否为multiple
function createElement$1 (tagName, vnode) {
  var elm = document.createElement(tagName);
  if (tagName !== 'select') {
    return elm
  }
  // false or null will remove the attribute but undefined will not
  if (vnode.data && vnode.data.attrs && vnode.data.attrs.multiple !== undefined) {
    elm.setAttribute('multiple', 'multiple');
  }
  return elm
}
// 创建有命名空间的dom
function createElementNS (namespace, tagName) {
  return document.createElementNS(namespaceMap[namespace], tagName)
}
// 创建文本节点
function createTextNode (text) {
  return document.createTextNode(text)
}
// 创建注释节点
function createComment (text) {
  return document.createComment(text)
}
// 插入子节点
function insertBefore (parentNode, newNode, referenceNode) {
  parentNode.insertBefore(newNode, referenceNode);
}
// 移除子节点
function removeChild (node, child) {
  node.removeChild(child);
}
// 尾部加入子节点
function appendChild (node, child) {
  node.appendChild(child);
}
// 获取父节点
function parentNode (node) {
  return node.parentNode
}
// 获取下一个兄弟节点
function nextSibling (node) {
  return node.nextSibling
}
// 获取元素的标签名
function tagName (node) {
  return node.tagName
}
// 设置文本
function setTextContent (node, text) {
  node.textContent = text;
}
// 设置默认属性
function setStyleScope (node, scopeId) {
  node.setAttribute(scopeId, '');
}

// 创建一个dom方法集合的冻结对象，
var nodeOps = Object.freeze({
    createElement: createElement$1,
    createElementNS: createElementNS,
    createTextNode: createTextNode,
    createComment: createComment,
    insertBefore: insertBefore,
    removeChild: removeChild,
    appendChild: appendChild,
    parentNode: parentNode,
    nextSibling: nextSibling,
    tagName: tagName,
    setTextContent: setTextContent,
    setStyleScope: setStyleScope
});

/*  */
// ref的方法集合，
var ref = {
  //创建
  create: function create (_, vnode) {
    registerRef(vnode);
  },
  //跟新，删除就ref,添加新ref
  update: function update (oldVnode, vnode) {
    if (oldVnode.data.ref !== vnode.data.ref) {
      registerRef(oldVnode, true);
      registerRef(vnode);
    }
  },
  //摧毁，删除ref
  destroy: function destroy (vnode) {
    registerRef(vnode, true);
  }
}
// 注册ref
function registerRef (vnode, isRemoval) {
  var key = vnode.data.ref;
  if (!isDef(key)) { return }

  var vm = vnode.context;
  var ref = vnode.componentInstance || vnode.elm;
  var refs = vm.$refs;
  // 移除
  if (isRemoval) {
    if (Array.isArray(refs[key])) {
      remove(refs[key], ref);
    } else if (refs[key] === ref) {
      refs[key] = undefined;
    }
  } else {
    // 在v-for里使用，refs[key]变成数组的方式
    if (vnode.data.refInFor) {
      if (!Array.isArray(refs[key])) {
        refs[key] = [ref];
      } else if (refs[key].indexOf(ref) < 0) {
        // $flow-disable-line
        refs[key].push(ref);
      }
    } else {
      refs[key] = ref;
    }
  }
}

/**
 * Virtual DOM patching algorithm based on Snabbdom by
 * Simon Friis Vindum (@paldepind)
 * Licensed under the MIT License
 * https://github.com/paldepind/snabbdom/blob/master/LICENSE
 *
 * modified by Evan You (@yyx990803)
 *
 * Not type-checking this because this file is perf-critical and the cost
 * of making flow understand it is not worth it.
 */

var emptyNode = new VNode('', {}, []);
var hooks = ['create', 'activate', 'update', 'remove', 'destroy'];
// vnode是否相同，包括key,tag,isComponent,data或者异步组件相同
function sameVnode (a, b) {
  return (
    a.key === b.key && (
      (
        a.tag === b.tag &&
        a.isComment === b.isComment &&
        isDef(a.data) === isDef(b.data) &&
        sameInputType(a, b)
      ) || (
        isTrue(a.isAsyncPlaceholder) &&
        a.asyncFactory === b.asyncFactory &&
        isUndef(b.asyncFactory.error)
      )
    )
  )
}
// 判断是输入框的type类型是否相同
function sameInputType (a, b) {
  if (a.tag !== 'input') { return true }
  var i;
  var typeA = isDef(i = a.data) && isDef(i = i.attrs) && i.type;
  var typeB = isDef(i = b.data) && isDef(i = i.attrs) && i.type;
  return typeA === typeB || isTextInputType(typeA) && isTextInputType(typeB)
}
// 数组范围内的元素key集合
function createKeyToOldIdx (children, beginIdx, endIdx) {
  var i, key;
  var map = {};
  for (i = beginIdx; i <= endIdx; ++i) {
    key = children[i].key;
    if (isDef(key)) { map[key] = i; }
  }
  return map
}
// 将组件集合内的各个生命周期的方法生成嵌套集合
function createPatchFunction (backend) {
  var i, j;
  var cbs = {};

  var modules = backend.modules;
  var nodeOps = backend.nodeOps;

  for (i = 0; i < hooks.length; ++i) {
    cbs[hooks[i]] = [];
    for (j = 0; j < modules.length; ++j) {
      if (isDef(modules[j][hooks[i]])) {
        cbs[hooks[i]].push(modules[j][hooks[i]]);
      }
    }
  }

  function emptyNodeAt (elm) {
    return new VNode(nodeOps.tagName(elm).toLowerCase(), {}, [], undefined, elm)
  }
  // 移除监听
  function createRmCb (childElm, listeners) {
    function remove () {
      if (--remove.listeners === 0) {
        removeNode(childElm);
      }
    }
    remove.listeners = listeners;
    return remove
  }
  // 移除元素
  function removeNode (el) {
    var parent = nodeOps.parentNode(el);
    // element may have already been removed due to v-html / v-text
    if (isDef(parent)) {
      nodeOps.removeChild(parent, el);
    }
  }
  // 检查是否是未知标签
  function isUnknownElement$$1 (vnode, inVPre) {
    return (
      !inVPre &&
      !vnode.ns &&
      !(
        config.ignoredElements.length &&
        config.ignoredElements.some(function (ignore) {
          return isRegExp(ignore)
            ? ignore.test(vnode.tag)
            : ignore === vnode.tag
        })
      ) &&
      config.isUnknownElement(vnode.tag)
    )
  }