代码大概6600-8600行

var validDivisionCharRE = /[\w).+\-_$\]]/;

function parseFilters (exp) {
  var inSingle = false;
  var inDouble = false;
  var inTemplateString = false;
  var inRegex = false;
  var curly = 0;
  var square = 0;
  var paren = 0;
  var lastFilterIndex = 0;
  var c, prev, i, expression, filters;

  for (i = 0; i < exp.length; i++) {
    prev = c;
    c = exp.charCodeAt(i);
    if (inSingle) {
      if (c === 0x27 && prev !== 0x5C) { inSingle = false; }
    } else if (inDouble) {
      if (c === 0x22 && prev !== 0x5C) { inDouble = false; }
    } else if (inTemplateString) {
      if (c === 0x60 && prev !== 0x5C) { inTemplateString = false; }
    } else if (inRegex) {
      if (c === 0x2f && prev !== 0x5C) { inRegex = false; }
    } else if (
      c === 0x7C && // pipe
      exp.charCodeAt(i + 1) !== 0x7C &&
      exp.charCodeAt(i - 1) !== 0x7C &&
      !curly && !square && !paren
    ) {
      if (expression === undefined) {
        // first filter, end of expression
        lastFilterIndex = i + 1;
        expression = exp.slice(0, i).trim();
      } else {
        pushFilter();
      }
    } else {
      switch (c) {
        case 0x22: inDouble = true; break         // "
        case 0x27: inSingle = true; break         // '
        case 0x60: inTemplateString = true; break // `
        case 0x28: paren++; break                 // (
        case 0x29: paren--; break                 // )
        case 0x5B: square++; break                // [
        case 0x5D: square--; break                // ]
        case 0x7B: curly++; break                 // {
        case 0x7D: curly--; break                 // }
      }
      if (c === 0x2f) { // /
        var j = i - 1;
        var p = (void 0);
        // find first non-whitespace prev char
        for (; j >= 0; j--) {
          p = exp.charAt(j);
          if (p !== ' ') { break }
        }
        if (!p || !validDivisionCharRE.test(p)) {
          inRegex = true;
        }
      }
    }
  }

  if (expression === undefined) {
    expression = exp.slice(0, i).trim();
  } else if (lastFilterIndex !== 0) {
    pushFilter();
  }

  function pushFilter () {
    (filters || (filters = [])).push(exp.slice(lastFilterIndex, i).trim());
    lastFilterIndex = i + 1;
  }

  if (filters) {
    for (i = 0; i < filters.length; i++) {
      expression = wrapFilter(expression, filters[i]);
    }
  }

  return expression
}
// filter区分名字和参数
function wrapFilter (exp, filter) {
  var i = filter.indexOf('(');
  if (i < 0) {
    // _f: resolveFilter
    return ("_f(\"" + filter + "\")(" + exp + ")")
  } else {
    var name = filter.slice(0, i);
    var args = filter.slice(i + 1);
    return ("_f(\"" + name + "\")(" + exp + (args !== ')' ? ',' + args : args))
  }
}

/*  */
// 解析错误信息
function baseWarn (msg) {
  console.error(("[Vue compiler]: " + msg));
}
// 匹配modules[keys]的通过条件的新数组
function pluckModuleFunction (
  modules,
  key
) {
  return modules
    ? modules.map(function (m) { return m[key]; }).filter(function (_) { return _; })
    : []
}
// 添加prop
function addProp (el, name, value) {
  (el.props || (el.props = [])).push({ name: name, value: value });
  el.plain = false;
}
// 添加属性 attr
function addAttr (el, name, value) {
  (el.attrs || (el.attrs = [])).push({ name: name, value: value });
  el.plain = false;
}

// add a raw attr (use this in preTransforms)
// 添加attrList,attrMap
function addRawAttr (el, name, value) {
  el.attrsMap[name] = value;
  el.attrsList.push({ name: name, value: value });
}
// 为元素添加指令
function addDirective (
  el,
  name,
  rawName,
  value,
  arg,
  modifiers
) {
  (el.directives || (el.directives = [])).push({ name: name, rawName: rawName, value: value, arg: arg, modifiers: modifiers });
  el.plain = false;
}
// 添加回调
function addHandler (
  el,
  name,
  value,
  modifiers,
  important,
  warn
) {
  modifiers = modifiers || emptyObject;
  // warn prevent and passive modifier
  /* istanbul ignore if */
  if (
    "development" !== 'production' && warn &&
    modifiers.prevent && modifiers.passive
  ) {
    warn(
      'passive and prevent can\'t be used together. ' +
      'Passive handler can\'t prevent default event.'
    );
  }

  // check capture modifier
  if (modifiers.capture) {
    delete modifiers.capture;
    name = '!' + name; // mark the event as captured
  }
  if (modifiers.once) {
    delete modifiers.once;
    name = '~' + name; // mark the event as once
  }
  /* istanbul ignore if */
  if (modifiers.passive) {
    delete modifiers.passive;
    name = '&' + name; // mark the event as passive
  }

  // normalize click.right and click.middle since they don't actually fire
  // this is technically browser-specific, but at least for now browsers are
  // the only target envs that have right/middle clicks.
  if (name === 'click') {
    if (modifiers.right) {
      name = 'contextmenu';
      delete modifiers.right;
    } else if (modifiers.middle) {
      name = 'mouseup';
    }
  }

  var events;
  if (modifiers.native) {
    delete modifiers.native;
    events = el.nativeEvents || (el.nativeEvents = {});
  } else {
    events = el.events || (el.events = {});
  }

  var newHandler = {
    value: value.trim()
  };
  if (modifiers !== emptyObject) {
    newHandler.modifiers = modifiers;
  }

  var handlers = events[name];
  /* istanbul ignore if */
  if (Array.isArray(handlers)) {
    important ? handlers.unshift(newHandler) : handlers.push(newHandler);
  } else if (handlers) {
    events[name] = important ? [newHandler, handlers] : [handlers, newHandler];
  } else {
    events[name] = newHandler;
  }

  el.plain = false;
}

function getBindingAttr (
  el,
  name,
  getStatic
) {
  var dynamicValue =
  // 获取 v-bind绑定的值并删除
    getAndRemoveAttr(el, ':' + name) ||
    getAndRemoveAttr(el, 'v-bind:' + name);
  if (dynamicValue != null) {
    return parseFilters(dynamicValue)
  } else if (getStatic !== false) {
    var staticValue = getAndRemoveAttr(el, name);
    if (staticValue != null) {
      return JSON.stringify(staticValue)
    }
  }
}

// note: this only removes the attr from the Array (attrsList) so that it
// doesn't get processed by processAttrs.
// By default it does NOT remove it from the map (attrsMap) because the map is
// needed during codegen.
// 将el.attrMap中el.attrsList中的属性删除
function getAndRemoveAttr (
  el,
  name,
  removeFromMap
) {
  var val;
  if ((val = el.attrsMap[name]) != null) {
    var list = el.attrsList;
    for (var i = 0, l = list.length; i < l; i++) {
      if (list[i].name === name) {
        list.splice(i, 1);
        break
      }
    }
  }
  if (removeFromMap) {
    delete el.attrsMap[name];
  }
  return val
}

/*  */

/**
 * Cross-platform code generation for component v-model
 */
// v-model解析
function genComponentModel (
  el,
  value,
  modifiers
) {
  var ref = modifiers || {};
  var number = ref.number;
  var trim = ref.trim;

  var baseValueExpression = '$$v';
  var valueExpression = baseValueExpression;
  if (trim) {
    valueExpression =
      "(typeof " + baseValueExpression + " === 'string'" +
      "? " + baseValueExpression + ".trim()" +
      ": " + baseValueExpression + ")";
  }
  if (number) {
    valueExpression = "_n(" + valueExpression + ")";
  }
  var assignment = genAssignmentCode(value, valueExpression);

  el.model = {
    value: ("(" + value + ")"),
    expression: ("\"" + value + "\""),
    callback: ("function (" + baseValueExpression + ") {" + assignment + "}")
  };
}

/**
 * Cross-platform codegen helper for generating v-model value assignment code.
 */
function genAssignmentCode (
  value,
  assignment
) {
  var res = parseModel(value);
  if (res.key === null) {
    return (value + "=" + assignment)
  } else {
    return ("$set(" + (res.exp) + ", " + (res.key) + ", " + assignment + ")")
  }
}

/**
 * Parse a v-model expression into a base path and a final key segment.
 * Handles both dot-path and possible square brackets.
 *
 * Possible cases:
 *
 * - test
 * - test[key]
 * - test[test1[key]]
 * - test["a"][key]
 * - xxx.test[a[a].test1[key]]
 * - test.xxx.a["asa"][test1[key]]
 *
 */

var len;
var str;
var chr;
var index$1;
var expressionPos;
var expressionEndPos;


// 
function parseModel (val) {
  // Fix https://github.com/vuejs/vue/pull/7730
  // allow v-model="obj.val " (trailing whitespace)
  val = val.trim();
  len = val.length;

  if (val.indexOf('[') < 0 || val.lastIndexOf(']') < len - 1) {
    index$1 = val.lastIndexOf('.');
    if (index$1 > -1) {
      return {
        exp: val.slice(0, index$1),
        key: '"' + val.slice(index$1 + 1) + '"'
      }
    } else {
      return {
        exp: val,
        key: null
      }
    }
  }

  str = val;
  index$1 = expressionPos = expressionEndPos = 0;

  while (!eof()) {
    chr = next();
    /* istanbul ignore if */
    if (isStringStart(chr)) {
      parseString(chr);
    } else if (chr === 0x5B) {
      parseBracket(chr);
    }
  }

  return {
    exp: val.slice(0, expressionPos),
    key: val.slice(expressionPos + 1, expressionEndPos)
  }
}
// 下一个字符
function next () {
  return str.charCodeAt(++index$1)
}
// 大于最后一个
function eof () {
  return index$1 >= len
}

function isStringStart (chr) {
  return chr === 0x22 || chr === 0x27
}

function parseBracket (chr) {
  var inBracket = 1;
  expressionPos = index$1;
  while (!eof()) {
    chr = next();
    if (isStringStart(chr)) {
      parseString(chr);
      continue
    }
    if (chr === 0x5B) { inBracket++; }
    if (chr === 0x5D) { inBracket--; }
    if (inBracket === 0) {
      expressionEndPos = index$1;
      break
    }
  }
}
// 解析字符串
function parseString (chr) {
  var stringQuote = chr;
  while (!eof()) {
    chr = next();
    if (chr === stringQuote) {
      break
    }
  }
}

/*  */

var warn$1;

// in some cases, the event used has to be determined at runtime
// so we used some reserved tokens during compile.
var RANGE_TOKEN = '__r';
var CHECKBOX_RADIO_TOKEN = '__c';

function model (
  el,
  dir,
  _warn
) {
  warn$1 = _warn;
  var value = dir.value;
  var modifiers = dir.modifiers;
  var tag = el.tag;
  var type = el.attrsMap.type;

  {
    // inputs with type="file" are read only and setting the input's
    // value will throw an error.
    if (tag === 'input' && type === 'file') {
      warn$1(
        "<" + (el.tag) + " v-model=\"" + value + "\" type=\"file\">:\n" +
        "File inputs are read only. Use a v-on:change listener instead."
      );
    }
  }

  if (el.component) {
    genComponentModel(el, value, modifiers);
    // component v-model doesn't need extra runtime
    return false
  } else if (tag === 'select') {
    genSelect(el, value, modifiers);
  } else if (tag === 'input' && type === 'checkbox') {
    genCheckboxModel(el, value, modifiers);
  } else if (tag === 'input' && type === 'radio') {
    genRadioModel(el, value, modifiers);
  } else if (tag === 'input' || tag === 'textarea') {
    genDefaultModel(el, value, modifiers);
  } else if (!config.isReservedTag(tag)) {
    genComponentModel(el, value, modifiers);
    // component v-model doesn't need extra runtime
    return false
  } else {
    warn$1(
      "<" + (el.tag) + " v-model=\"" + value + "\">: " +
      "v-model is not supported on this element type. " +
      'If you are working with contenteditable, it\'s recommended to ' +
      'wrap a library dedicated for that purpose inside a custom component.'
    );
  }

  // ensure runtime directive metadata
  return true
}
// 解析checkbox的 v-model
function genCheckboxModel (
  el,
  value,
  modifiers
) {
  var number = modifiers && modifiers.number;
  var valueBinding = getBindingAttr(el, 'value') || 'null';
  var trueValueBinding = getBindingAttr(el, 'true-value') || 'true';
  var falseValueBinding = getBindingAttr(el, 'false-value') || 'false';
  addProp(el, 'checked',
    "Array.isArray(" + value + ")" +
    "?_i(" + value + "," + valueBinding + ")>-1" + (
      trueValueBinding === 'true'
        ? (":(" + value + ")")
        : (":_q(" + value + "," + trueValueBinding + ")")
    )
  );
  addHandler(el, 'change',
    "var $$a=" + value + "," +
        '$$el=$event.target,' +
        "$$c=$$el.checked?(" + trueValueBinding + "):(" + falseValueBinding + ");" +
    'if(Array.isArray($$a)){' +
      "var $$v=" + (number ? '_n(' + valueBinding + ')' : valueBinding) + "," +
          '$$i=_i($$a,$$v);' +
      "if($$el.checked){$$i<0&&(" + (genAssignmentCode(value, '$$a.concat([$$v])')) + ")}" +
      "else{$$i>-1&&(" + (genAssignmentCode(value, '$$a.slice(0,$$i).concat($$a.slice($$i+1))')) + ")}" +
    "}else{" + (genAssignmentCode(value, '$$c')) + "}",
    null, true
  );
}
// 解析 raido的v-model
function genRadioModel (
  el,
  value,
  modifiers
) {
  var number = modifiers && modifiers.number;
  var valueBinding = getBindingAttr(el, 'value') || 'null';
  valueBinding = number ? ("_n(" + valueBinding + ")") : valueBinding;
  addProp(el, 'checked', ("_q(" + value + "," + valueBinding + ")"));
  addHandler(el, 'change', genAssignmentCode(value, valueBinding), null, true);
}

function genSelect (
  el,
  value,
  modifiers
) {
  var number = modifiers && modifiers.number;
  var selectedVal = "Array.prototype.filter" +
    ".call($event.target.options,function(o){return o.selected})" +
    ".map(function(o){var val = \"_value\" in o ? o._value : o.value;" +
    "return " + (number ? '_n(val)' : 'val') + "})";

  var assignment = '$event.target.multiple ? $$selectedVal : $$selectedVal[0]';
  var code = "var $$selectedVal = " + selectedVal + ";";
  code = code + " " + (genAssignmentCode(value, assignment));
  addHandler(el, 'change', code, null, true);
}
// v-model 默认值
function genDefaultModel (
  el,
  value,
  modifiers
) {
  var type = el.attrsMap.type;

  // warn if v-bind:value conflicts with v-model
  // except for inputs with v-bind:type
  {
    var value$1 = el.attrsMap['v-bind:value'] || el.attrsMap[':value'];
    var typeBinding = el.attrsMap['v-bind:type'] || el.attrsMap[':type'];
    if (value$1 && !typeBinding) {
      var binding = el.attrsMap['v-bind:value'] ? 'v-bind:value' : ':value';
      warn$1(
        binding + "=\"" + value$1 + "\" conflicts with v-model on the same element " +
        'because the latter already expands to a value binding internally'
      );
    }
  }

  var ref = modifiers || {};
  var lazy = ref.lazy;
  var number = ref.number;
  var trim = ref.trim;
  var needCompositionGuard = !lazy && type !== 'range';
  var event = lazy
    ? 'change'
    : type === 'range'
      ? RANGE_TOKEN
      : 'input';

  var valueExpression = '$event.target.value';
  if (trim) {
    valueExpression = "$event.target.value.trim()";
  }
  if (number) {
    valueExpression = "_n(" + valueExpression + ")";
  }

  var code = genAssignmentCode(value, valueExpression);
  if (needCompositionGuard) {
    code = "if($event.target.composing)return;" + code;
  }

  addProp(el, 'value', ("(" + value + ")"));
  addHandler(el, event, code, null, true);
  if (trim || number) {
    addHandler(el, 'blur', '$forceUpdate()');
  }
}

/*  */

// normalize v-model event tokens that can only be determined at runtime.
// it's important to place the event as the first in the array because
// the whole point is ensuring the v-model callback gets called before
// user-attached handlers.
// v-model改变的事件
function normalizeEvents (on) {
  /* istanbul ignore if */
  if (isDef(on[RANGE_TOKEN])) {
    // IE input[type=range] only supports `change` event
    var event = isIE ? 'change' : 'input';
    on[event] = [].concat(on[RANGE_TOKEN], on[event] || []);
    delete on[RANGE_TOKEN];
  }
  // This was originally intended to fix #4521 but no longer necessary
  // after 2.5. Keeping it for backwards compat with generated code from < 2.4
  /* istanbul ignore if */
  if (isDef(on[CHECKBOX_RADIO_TOKEN])) {
    on.change = [].concat(on[CHECKBOX_RADIO_TOKEN], on.change || []);
    delete on[CHECKBOX_RADIO_TOKEN];
  }
}

var target$1;

function createOnceHandler (handler, event, capture) {
  var _target = target$1; // save current target element in closure
  return function onceHandler () {
    var res = handler.apply(null, arguments);
    if (res !== null) {
      remove$2(event, onceHandler, capture, _target);
    }
  }
}
// 将函数和事件名进行绑定
function add$1 (
  event,
  handler,
  once$$1,
  capture,
  passive
) {
  handler = withMacroTask(handler);
  if (once$$1) { handler = createOnceHandler(handler, event, capture); }
  target$1.addEventListener(
    event,
    handler,
    supportsPassive
      ? { capture: capture, passive: passive }
      : capture
  );
}
// 解绑事件
function remove$2 (
  event,
  handler,
  capture,
  _target
) {
  (_target || target$1).removeEventListener(
    event,
    handler._withTask || handler,
    capture
  );
}
// 跟新监听事件
function updateDOMListeners (oldVnode, vnode) {
  if (isUndef(oldVnode.data.on) && isUndef(vnode.data.on)) {
    return
  }
  var on = vnode.data.on || {};
  var oldOn = oldVnode.data.on || {};
  target$1 = vnode.elm;
  normalizeEvents(on);
  updateListeners(on, oldOn, add$1, remove$2, vnode.context);
  target$1 = undefined;
}

var events = {
  create: updateDOMListeners,
  update: updateDOMListeners
}

/*  */
// 跟新props
function updateDOMProps (oldVnode, vnode) {
  if (isUndef(oldVnode.data.domProps) && isUndef(vnode.data.domProps)) {
    return
  }
  var key, cur;
  var elm = vnode.elm;
  var oldProps = oldVnode.data.domProps || {};
  var props = vnode.data.domProps || {};
  // clone observed objects, as the user probably wants to mutate it
  if (isDef(props.__ob__)) {
    props = vnode.data.domProps = extend({}, props);
  }

  for (key in oldProps) {
    if (isUndef(props[key])) {
      elm[key] = '';
    }
  }
  for (key in props) {
    cur = props[key];
    // ignore children if the node has textContent or innerHTML,
    // as these will throw away existing DOM nodes and cause removal errors
    // on subsequent patches (#3360)
    if (key === 'textContent' || key === 'innerHTML') {
      if (vnode.children) { vnode.children.length = 0; }
      if (cur === oldProps[key]) { continue }
      // #6601 work around Chrome version <= 55 bug where single textNode
      // replaced by innerHTML/textContent retains its parentNode property
      if (elm.childNodes.length === 1) {
        elm.removeChild(elm.childNodes[0]);
      }
    }

    if (key === 'value') {
      // store value as _value as well since
      // non-string values will be stringified
      elm._value = cur;
      // avoid resetting cursor position when value is the same
      var strCur = isUndef(cur) ? '' : String(cur);
      if (shouldUpdateValue(elm, strCur)) {
        elm.value = strCur;
      }
    } else {
      elm[key] = cur;
    }
  }
}

// check platforms/web/util/attrs.js acceptValue

// 判断你是否跟新value
function shouldUpdateValue (elm, checkVal) {
  return (!elm.composing && (
    elm.tagName === 'OPTION' ||
    isNotInFocusAndDirty(elm, checkVal) ||
    isDirtyWithModifiers(elm, checkVal)
  ))
}

function isNotInFocusAndDirty (elm, checkVal) {
  // return true when textbox (.number and .trim) loses focus and its value is
  // not equal to the updated value
  var notInFocus = true;
  // #6157
  // work around IE bug when accessing document.activeElement in an iframe
  try { notInFocus = document.activeElement !== elm; } catch (e) {}
  return notInFocus && elm.value !== checkVal
}

function isDirtyWithModifiers (elm, newVal) {
  var value = elm.value;
  var modifiers = elm._vModifiers; // injected by v-model runtime
  if (isDef(modifiers)) {
    if (modifiers.lazy) {
      // inputs with lazy should only be updated when not in focus
      return false
    }
    if (modifiers.number) {
      return toNumber(value) !== toNumber(newVal)
    }
    if (modifiers.trim) {
      return value.trim() !== newVal.trim()
    }
  }
  return value !== newVal
}

var domProps = {
  create: updateDOMProps,
  update: updateDOMProps
}

/*  */

var parseStyleText = cached(function (cssText) {
  var res = {};
  var listDelimiter = /;(?![^(]*\))/g;
  var propertyDelimiter = /:(.+)/;
  cssText.split(listDelimiter).forEach(function (item) {
    if (item) {
      var tmp = item.split(propertyDelimiter);
      tmp.length > 1 && (res[tmp[0].trim()] = tmp[1].trim());
    }
  });
  return res
});

// merge static and dynamic style data on the same vnode
function normalizeStyleData (data) {
  var style = normalizeStyleBinding(data.style);
  // static style is pre-processed into an object during compilation
  // and is always a fresh object, so it's safe to merge into it
  return data.staticStyle
    ? extend(data.staticStyle, style)
    : style
}

// normalize possible array / string values into Object
function normalizeStyleBinding (bindingStyle) {
  if (Array.isArray(bindingStyle)) {
    return toObject(bindingStyle)
  }
  if (typeof bindingStyle === 'string') {
    return parseStyleText(bindingStyle)
  }
  return bindingStyle
}

/**
 * parent component style should be after child's
 * so that parent component's style could override it
 */
function getStyle (vnode, checkChild) {
  var res = {};
  var styleData;

  if (checkChild) {
    var childNode = vnode;
    while (childNode.componentInstance) {
      childNode = childNode.componentInstance._vnode;
      if (
        childNode && childNode.data &&
        (styleData = normalizeStyleData(childNode.data))
      ) {
        extend(res, styleData);
      }
    }
  }

  if ((styleData = normalizeStyleData(vnode.data))) {
    extend(res, styleData);
  }

  var parentNode = vnode;
  while ((parentNode = parentNode.parent)) {
    if (parentNode.data && (styleData = normalizeStyleData(parentNode.data))) {
      extend(res, styleData);
    }
  }
  return res
}

/*  */

var cssVarRE = /^--/;
var importantRE = /\s*!important$/;
var setProp = function (el, name, val) {
  /* istanbul ignore if */
  if (cssVarRE.test(name)) {
    el.style.setProperty(name, val);
  } else if (importantRE.test(val)) {
    el.style.setProperty(name, val.replace(importantRE, ''), 'important');
  } else {
    var normalizedName = normalize(name);
    if (Array.isArray(val)) {
      // Support values array created by autoprefixer, e.g.
      // {display: ["-webkit-box", "-ms-flexbox", "flex"]}
      // Set them one by one, and the browser will only set those it can recognize
      for (var i = 0, len = val.length; i < len; i++) {
        el.style[normalizedName] = val[i];
      }
    } else {
      el.style[normalizedName] = val;
    }
  }
};

var vendorNames = ['Webkit', 'Moz', 'ms'];

var emptyStyle;
var normalize = cached(function (prop) {
  emptyStyle = emptyStyle || document.createElement('div').style;
  prop = camelize(prop);
  if (prop !== 'filter' && (prop in emptyStyle)) {
    return prop
  }
  var capName = prop.charAt(0).toUpperCase() + prop.slice(1);
  for (var i = 0; i < vendorNames.length; i++) {
    var name = vendorNames[i] + capName;
    if (name in emptyStyle) {
      return name
    }
  }
});

function updateStyle (oldVnode, vnode) {
  var data = vnode.data;
  var oldData = oldVnode.data;

  if (isUndef(data.staticStyle) && isUndef(data.style) &&
    isUndef(oldData.staticStyle) && isUndef(oldData.style)
  ) {
    return
  }

  var cur, name;
  var el = vnode.elm;
  var oldStaticStyle = oldData.staticStyle;
  var oldStyleBinding = oldData.normalizedStyle || oldData.style || {};

  // if static style exists, stylebinding already merged into it when doing normalizeStyleData
  var oldStyle = oldStaticStyle || oldStyleBinding;

  var style = normalizeStyleBinding(vnode.data.style) || {};

  // store normalized style under a different key for next diff
  // make sure to clone it if it's reactive, since the user likely wants
  // to mutate it.
  vnode.data.normalizedStyle = isDef(style.__ob__)
    ? extend({}, style)
    : style;

  var newStyle = getStyle(vnode, true);

  for (name in oldStyle) {
    if (isUndef(newStyle[name])) {
      setProp(el, name, '');
    }
  }
  for (name in newStyle) {
    cur = newStyle[name];
    if (cur !== oldStyle[name]) {
      // ie9 setting to null has no effect, must use empty string
      setProp(el, name, cur == null ? '' : cur);
    }
  }
}

var style = {
  create: updateStyle,
  update: updateStyle
}

/*  */

/**
 * Add class with compatibility for SVG since classList is not supported on
 * SVG elements in IE
 */
// 
function addClass (el, cls) {
  /* istanbul ignore if */
  if (!cls || !(cls = cls.trim())) {
    return
  }

  /* istanbul ignore else */
  if (el.classList) {
    if (cls.indexOf(' ') > -1) {
      cls.split(/\s+/).forEach(function (c) { return el.classList.add(c); });
    } else {
      el.classList.add(cls);
    }
  } else {
    var cur = " " + (el.getAttribute('class') || '') + " ";
    if (cur.indexOf(' ' + cls + ' ') < 0) {
      el.setAttribute('class', (cur + cls).trim());
    }
  }
}

/**
 * Remove class with compatibility for SVG since classList is not supported on
 * SVG elements in IE
 */
function removeClass (el, cls) {
  /* istanbul ignore if */
  if (!cls || !(cls = cls.trim())) {
    return
  }

  /* istanbul ignore else */
  if (el.classList) {
    if (cls.indexOf(' ') > -1) {
      cls.split(/\s+/).forEach(function (c) { return el.classList.remove(c); });
    } else {
      el.classList.remove(cls);
    }
    if (!el.classList.length) {
      el.removeAttribute('class');
    }
  } else {
    var cur = " " + (el.getAttribute('class') || '') + " ";
    var tar = ' ' + cls + ' ';
    while (cur.indexOf(tar) >= 0) {
      cur = cur.replace(tar, ' ');
    }
    cur = cur.trim();
    if (cur) {
      el.setAttribute('class', cur);
    } else {
      el.removeAttribute('class');
    }
  }
}

/*  */

function resolveTransition (def) {
  if (!def) {
    return
  }
  /* istanbul ignore else */
  if (typeof def === 'object') {
    var res = {};
    if (def.css !== false) {
      extend(res, autoCssTransition(def.name || 'v'));
    }
    extend(res, def);
    return res
  } else if (typeof def === 'string') {
    return autoCssTransition(def)
  }
}

var autoCssTransition = cached(function (name) {
  return {
    enterClass: (name + "-enter"),
    enterToClass: (name + "-enter-to"),
    enterActiveClass: (name + "-enter-active"),
    leaveClass: (name + "-leave"),
    leaveToClass: (name + "-leave-to"),
    leaveActiveClass: (name + "-leave-active")
  }
});

var hasTransition = inBrowser && !isIE9;
var TRANSITION = 'transition';
var ANIMATION = 'animation';

// Transition property/event sniffing
var transitionProp = 'transition';
var transitionEndEvent = 'transitionend';
var animationProp = 'animation';
var animationEndEvent = 'animationend';
if (hasTransition) {
  /* istanbul ignore if */
  if (window.ontransitionend === undefined &&
    window.onwebkittransitionend !== undefined
  ) {
    transitionProp = 'WebkitTransition';
    transitionEndEvent = 'webkitTransitionEnd';
  }
  if (window.onanimationend === undefined &&
    window.onwebkitanimationend !== undefined
  ) {
    animationProp = 'WebkitAnimation';
    animationEndEvent = 'webkitAnimationEnd';
  }
}

// binding to window is necessary to make hot reload work in IE in strict mode
var raf = inBrowser
  ? window.requestAnimationFrame
    ? window.requestAnimationFrame.bind(window)
    : setTimeout
  : /* istanbul ignore next */ function (fn) { return fn(); };

function nextFrame (fn) {
  raf(function () {
    raf(fn);
  });
}

function addTransitionClass (el, cls) {
  var transitionClasses = el._transitionClasses || (el._transitionClasses = []);
  if (transitionClasses.indexOf(cls) < 0) {
    transitionClasses.push(cls);
    addClass(el, cls);
  }
}

function removeTransitionClass (el, cls) {
  if (el._transitionClasses) {
    remove(el._transitionClasses, cls);
  }
  removeClass(el, cls);
}
// 动画结束
function whenTransitionEnds (
  el,
  expectedType,
  cb
) {
  var ref = getTransitionInfo(el, expectedType);
  var type = ref.type;
  var timeout = ref.timeout;
  var propCount = ref.propCount;
  if (!type) { return cb() }
  var event = type === TRANSITION ? transitionEndEvent : animationEndEvent;
  var ended = 0;
  var end = function () {
    el.removeEventListener(event, onEnd);
    cb();
  };
  var onEnd = function (e) {
    if (e.target === el) {
      if (++ended >= propCount) {
        end();
      }
    }
  };
  setTimeout(function () {
    if (ended < propCount) {
      end();
    }
  }, timeout + 1);
  el.addEventListener(event, onEnd);
}

var transformRE = /\b(transform|all)(,|$)/;
// 获取dom属性上自带的动画
function getTransitionInfo (el, expectedType) {
  var styles = window.getComputedStyle(el);
  var transitionDelays = styles[transitionProp + 'Delay'].split(', ');
  var transitionDurations = styles[transitionProp + 'Duration'].split(', ');
  var transitionTimeout = getTimeout(transitionDelays, transitionDurations);
  var animationDelays = styles[animationProp + 'Delay'].split(', ');
  var animationDurations = styles[animationProp + 'Duration'].split(', ');
  var animationTimeout = getTimeout(animationDelays, animationDurations);

  var type;
  var timeout = 0;
  var propCount = 0;
  /* istanbul ignore if */
  if (expectedType === TRANSITION) {
    if (transitionTimeout > 0) {
      type = TRANSITION;
      timeout = transitionTimeout;
      propCount = transitionDurations.length;
    }
  } else if (expectedType === ANIMATION) {
    if (animationTimeout > 0) {
      type = ANIMATION;
      timeout = animationTimeout;
      propCount = animationDurations.length;
    }
  } else {
    timeout = Math.max(transitionTimeout, animationTimeout);
    type = timeout > 0
      ? transitionTimeout > animationTimeout
        ? TRANSITION
        : ANIMATION
      : null;
    propCount = type
      ? type === TRANSITION
        ? transitionDurations.length
        : animationDurations.length
      : 0;
  }
  var hasTransform =
    type === TRANSITION &&
    transformRE.test(styles[transitionProp + 'Property']);
  return {
    type: type,
    timeout: timeout,
    propCount: propCount,
    hasTransform: hasTransform
  }
}
// 获取延迟时间
function getTimeout (delays, durations) {
  /* istanbul ignore next */
  while (delays.length < durations.length) {
    delays = delays.concat(delays);
  }

  return Math.max.apply(null, durations.map(function (d, i) {
    return toMs(d) + toMs(delays[i])
  }))
}

function toMs (s) {
  return Number(s.slice(0, -1)) * 1000
}

/*  */
// 动画开始一系列操作，不想看了
function enter (vnode, toggleDisplay) {
  var el = vnode.elm;

  // call leave callback now
  if (isDef(el._leaveCb)) {
    el._leaveCb.cancelled = true;
    el._leaveCb();
  }

  var data = resolveTransition(vnode.data.transition);
  if (isUndef(data)) {
    return
  }

  /* istanbul ignore if */
  if (isDef(el._enterCb) || el.nodeType !== 1) {
    return
  }

  var css = data.css;
  var type = data.type;
  var enterClass = data.enterClass;
  var enterToClass = data.enterToClass;
  var enterActiveClass = data.enterActiveClass;
  var appearClass = data.appearClass;
  var appearToClass = data.appearToClass;
  var appearActiveClass = data.appearActiveClass;
  var beforeEnter = data.beforeEnter;
  var enter = data.enter;
  var afterEnter = data.afterEnter;
  var enterCancelled = data.enterCancelled;
  var beforeAppear = data.beforeAppear;
  var appear = data.appear;
  var afterAppear = data.afterAppear;
  var appearCancelled = data.appearCancelled;
  var duration = data.duration;

  // activeInstance will always be the <transition> component managing this
  // transition. One edge case to check is when the <transition> is placed
  // as the root node of a child component. In that case we need to check
  // <transition>'s parent for appear check.
  var context = activeInstance;
  var transitionNode = activeInstance.$vnode;
  while (transitionNode && transitionNode.parent) {
    transitionNode = transitionNode.parent;
    context = transitionNode.context;
  }

  var isAppear = !context._isMounted || !vnode.isRootInsert;

  if (isAppear && !appear && appear !== '') {
    return
  }

  var startClass = isAppear && appearClass
    ? appearClass
    : enterClass;
  var activeClass = isAppear && appearActiveClass
    ? appearActiveClass
    : enterActiveClass;
  var toClass = isAppear && appearToClass
    ? appearToClass
    : enterToClass;

  var beforeEnterHook = isAppear
    ? (beforeAppear || beforeEnter)
    : beforeEnter;
  var enterHook = isAppear
    ? (typeof appear === 'function' ? appear : enter)
    : enter;
  var afterEnterHook = isAppear
    ? (afterAppear || afterEnter)
    : afterEnter;
  var enterCancelledHook = isAppear
    ? (appearCancelled || enterCancelled)
    : enterCancelled;

  var explicitEnterDuration = toNumber(
    isObject(duration)
      ? duration.enter
      : duration
  );

  if ("development" !== 'production' && explicitEnterDuration != null) {
    checkDuration(explicitEnterDuration, 'enter', vnode);
  }

  var expectsCSS = css !== false && !isIE9;
  var userWantsControl = getHookArgumentsLength(enterHook);

  var cb = el._enterCb = once(function () {
    if (expectsCSS) {
      removeTransitionClass(el, toClass);
      removeTransitionClass(el, activeClass);
    }
    if (cb.cancelled) {
      if (expectsCSS) {
        removeTransitionClass(el, startClass);
      }
      enterCancelledHook && enterCancelledHook(el);
    } else {
      afterEnterHook && afterEnterHook(el);
    }
    el._enterCb = null;
  });

  if (!vnode.data.show) {
    // remove pending leave element on enter by injecting an insert hook
    mergeVNodeHook(vnode, 'insert', function () {
      var parent = el.parentNode;
      var pendingNode = parent && parent._pending && parent._pending[vnode.key];
      if (pendingNode &&
        pendingNode.tag === vnode.tag &&
        pendingNode.elm._leaveCb
      ) {
        pendingNode.elm._leaveCb();
      }
      enterHook && enterHook(el, cb);
    });
  }

  // start enter transition
  beforeEnterHook && beforeEnterHook(el);
  if (expectsCSS) {
    addTransitionClass(el, startClass);
    addTransitionClass(el, activeClass);
    nextFrame(function () {
      removeTransitionClass(el, startClass);
      if (!cb.cancelled) {
        addTransitionClass(el, toClass);
        if (!userWantsControl) {
          if (isValidDuration(explicitEnterDuration)) {
            setTimeout(cb, explicitEnterDuration);
          } else {
            whenTransitionEnds(el, type, cb);
          }
        }
      }
    });
  }

  if (vnode.data.show) {
    toggleDisplay && toggleDisplay();
    enterHook && enterHook(el, cb);
  }

  if (!expectsCSS && !userWantsControl) {
    cb();
  }
}
// leave动画函数
function leave (vnode, rm) {
  var el = vnode.elm;

  // call enter callback now
  if (isDef(el._enterCb)) {
    el._enterCb.cancelled = true;
    el._enterCb();
  }

  var data = resolveTransition(vnode.data.transition);
  if (isUndef(data) || el.nodeType !== 1) {
    return rm()
  }

  /* istanbul ignore if */
  if (isDef(el._leaveCb)) {
    return
  }

  var css = data.css;
  var type = data.type;
  var leaveClass = data.leaveClass;
  var leaveToClass = data.leaveToClass;
  var leaveActiveClass = data.leaveActiveClass;
  var beforeLeave = data.beforeLeave;
  var leave = data.leave;
  var afterLeave = data.afterLeave;
  var leaveCancelled = data.leaveCancelled;
  var delayLeave = data.delayLeave;
  var duration = data.duration;

  var expectsCSS = css !== false && !isIE9;
  var userWantsControl = getHookArgumentsLength(leave);

  var explicitLeaveDuration = toNumber(
    isObject(duration)
      ? duration.leave
      : duration
  );

  if ("development" !== 'production' && isDef(explicitLeaveDuration)) {
    checkDuration(explicitLeaveDuration, 'leave', vnode);
  }

  var cb = el._leaveCb = once(function () {
    if (el.parentNode && el.parentNode._pending) {
      el.parentNode._pending[vnode.key] = null;
    }
    if (expectsCSS) {
      removeTransitionClass(el, leaveToClass);
      removeTransitionClass(el, leaveActiveClass);
    }
    if (cb.cancelled) {
      if (expectsCSS) {
        removeTransitionClass(el, leaveClass);
      }
      leaveCancelled && leaveCancelled(el);
    } else {
      rm();
      afterLeave && afterLeave(el);
    }
    el._leaveCb = null;
  });

  if (delayLeave) {
    delayLeave(performLeave);
  } else {
    performLeave();
  }
  // 离开动画
  function performLeave () {
    // the delayed leave may have already been cancelled
    if (cb.cancelled) {
      return
    }
    // record leaving element
    if (!vnode.data.show) {
      (el.parentNode._pending || (el.parentNode._pending = {}))[(vnode.key)] = vnode;
    }
    //离开之前
    beforeLeave && beforeLeave(el);
    if (expectsCSS) {
      //离开动画
      addTransitionClass(el, leaveClass);
      // 离开激活动画
      addTransitionClass(el, leaveActiveClass);
      // 结束动画
      nextFrame(function () {
        //移除离开动画
        removeTransitionClass(el, leaveClass);
        if (!cb.cancelled) {
          //添加离开过度结束的动画
          addTransitionClass(el, leaveToClass);
          if (!userWantsControl) {
            // 延迟执行函数
            if (isValidDuration(explicitLeaveDuration)) {
              setTimeout(cb, explicitLeaveDuration);
            } else {
              whenTransitionEnds(el, type, cb);
            }
          }
        }
      });
    }
    // 离开回调函数
    leave && leave(el, cb);
    if (!expectsCSS && !userWantsControl) {
      cb();
    }
  }
}

// only used in dev mode
function checkDuration (val, name, vnode) {
  // 动画时间应该是数字类型
  if (typeof val !== 'number') {
    warn(
      "<transition> explicit " + name + " duration is not a valid number - " +
      "got " + (JSON.stringify(val)) + ".",
      vnode.context
    );
  } else if (isNaN(val)) {
    warn(
      "<transition> explicit " + name + " duration is NaN - " +
      'the duration expression might be incorrect.',
      vnode.context
    );
  }
}
// 是否是合法的动画时间
function isValidDuration (val) {
  return typeof val === 'number' && !isNaN(val)
}

/**
 * Normalize a transition hook's argument length. The hook may be:
 * - a merged hook (invoker) with the original in .fns
 * - a wrapped component method (check ._length)
 * - a plain function (.length)
 */
//获取生命周期中函数的传参长度
function getHookArgumentsLength (fn) {
  if (isUndef(fn)) {
    return false
  }
  var invokerFns = fn.fns;
  if (isDef(invokerFns)) {
    // invoker
    return getHookArgumentsLength(
      Array.isArray(invokerFns)
        ? invokerFns[0]
        : invokerFns
    )
  } else {
    return (fn._length || fn.length) > 1
  }
}
// 判断是否影藏，不是进入enter方法
function _enter (_, vnode) {
  if (vnode.data.show !== true) {
    enter(vnode);
  }
}
// 设置transition的几个方法
var transition = inBrowser ? {
  create: _enter,
  activate: _enter,
  // 动画移除的时候就是执行回调函数
  remove: function remove$$1 (vnode, rm) {
    /* istanbul ignore else */
    if (vnode.data.show !== true) {
      leave(vnode, rm);
    } else {
      rm();
    }
  }
} : {}

var platformModules = [
  attrs,
  klass,
  events,
  domProps,
  style,
  transition
]

/*  */

// the directive module should be applied last, after all
// built-in modules have been applied.
var modules = platformModules.concat(baseModules);

var patch = createPatchFunction({ nodeOps: nodeOps, modules: modules });

/**
 * Not type checking this file because flow doesn't like attaching
 * properties to Elements.
 */

/* istanbul ignore if */
if (isIE9) {
  // http://www.matts411.com/post/internet-explorer-9-oninput/
  document.addEventListener('selectionchange', function () {
    var el = document.activeElement;
    if (el && el.vmodel) {
      trigger(el, 'input');
    }
  });
}

var directive = {
  inserted: function inserted (el, binding, vnode, oldVnode) {
    if (vnode.tag === 'select') {
      // #6903
      if (oldVnode.elm && !oldVnode.elm._vOptions) {
        mergeVNodeHook(vnode, 'postpatch', function () {
          directive.componentUpdated(el, binding, vnode);
        });
      } else {
        setSelected(el, binding, vnode.context);
      }
      el._vOptions = [].map.call(el.options, getValue);
    } else if (vnode.tag === 'textarea' || isTextInputType(el.type)) {
      el._vModifiers = binding.modifiers;
      if (!binding.modifiers.lazy) {
        el.addEventListener('compositionstart', onCompositionStart);
        el.addEventListener('compositionend', onCompositionEnd);
        // Safari < 10.2 & UIWebView doesn't fire compositionend when
        // switching focus before confirming composition choice
        // this also fixes the issue where some browsers e.g. iOS Chrome
        // fires "change" instead of "input" on autocomplete.
        el.addEventListener('change', onCompositionEnd);
        /* istanbul ignore if */
        if (isIE9) {
          el.vmodel = true;
        }
      }
    }
  },

  componentUpdated: function componentUpdated (el, binding, vnode) {
    if (vnode.tag === 'select') {
      setSelected(el, binding, vnode.context);
      // in case the options rendered by v-for have changed,
      // it's possible that the value is out-of-sync with the rendered options.
      // detect such cases and filter out values that no longer has a matching
      // option in the DOM.
      var prevOptions = el._vOptions;
      var curOptions = el._vOptions = [].map.call(el.options, getValue);
      if (curOptions.some(function (o, i) { return !looseEqual(o, prevOptions[i]); })) {
        // trigger change event if
        // no matching option found for at least one value
        var needReset = el.multiple
          ? binding.value.some(function (v) { return hasNoMatchingOption(v, curOptions); })
          : binding.value !== binding.oldValue && hasNoMatchingOption(binding.value, curOptions);
        if (needReset) {
          trigger(el, 'change');
        }
      }
    }
  }
};

function setSelected (el, binding, vm) {
  actuallySetSelected(el, binding, vm);
  /* istanbul ignore if */
  if (isIE || isEdge) {
    setTimeout(function () {
      actuallySetSelected(el, binding, vm);
    }, 0);
  }
}

function actuallySetSelected (el, binding, vm) {
  var value = binding.value;
  var isMultiple = el.multiple;
  if (isMultiple && !Array.isArray(value)) {
    "development" !== 'production' && warn(
      "<select multiple v-model=\"" + (binding.expression) + "\"> " +
      "expects an Array value for its binding, but got " + (Object.prototype.toString.call(value).slice(8, -1)),
      vm
    );
    return
  }
  var selected, option;
  for (var i = 0, l = el.options.length; i < l; i++) {
    option = el.options[i];
    if (isMultiple) {
      selected = looseIndexOf(value, getValue(option)) > -1;
      if (option.selected !== selected) {
        option.selected = selected;
      }
    } else {
      if (looseEqual(getValue(option), value)) {
        if (el.selectedIndex !== i) {
          el.selectedIndex = i;
        }
        return
      }
    }
  }
  if (!isMultiple) {
    el.selectedIndex = -1;
  }
}
// select options移除相同的
function hasNoMatchingOption (value, options) {
  return options.every(function (o) { return !looseEqual(o, value); })
}
// 获取value
function getValue (option) {
  return '_value' in option
    ? option._value
    : option.value
}
// input事件开始
function onCompositionStart (e) {
  e.target.composing = true;
}
// input事件结束
function onCompositionEnd (e) {
  // prevent triggering an input event for no reason
  if (!e.target.composing) { return }
  e.target.composing = false;
  trigger(e.target, 'input');
}
// 模拟事件方法
function trigger (el, type) {
  var e = document.createEvent('HTMLEvents');
  e.initEvent(type, true, true);
  el.dispatchEvent(e);
}

/*  */

// recursively search for possible transition defined inside the component root
function locateNode (vnode) {
  return vnode.componentInstance && (!vnode.data || !vnode.data.transition)
    ? locateNode(vnode.componentInstance._vnode)
    : vnode
}
// 元素开始展示出来的方法
var show = {
  bind: function bind (el, ref, vnode) {
    var value = ref.value;

    vnode = locateNode(vnode);
    var transition$$1 = vnode.data && vnode.data.transition;
    var originalDisplay = el.__vOriginalDisplay =
      el.style.display === 'none' ? '' : el.style.display;
    if (value && transition$$1) {
      vnode.data.show = true;
      enter(vnode, function () {
        el.style.display = originalDisplay;
      });
    } else {
      el.style.display = value ? originalDisplay : 'none';
    }
  },

  update: function update (el, ref, vnode) {
    var value = ref.value;
    var oldValue = ref.oldValue;

    /* istanbul ignore if */
    if (!value === !oldValue) { return }
    vnode = locateNode(vnode);
    var transition$$1 = vnode.data && vnode.data.transition;
    if (transition$$1) {
      vnode.data.show = true;
      if (value) {
        enter(vnode, function () {
          el.style.display = el.__vOriginalDisplay;
        });
      } else {
        leave(vnode, function () {
          el.style.display = 'none';
        });
      }
    } else {
      el.style.display = value ? el.__vOriginalDisplay : 'none';
    }
  },

  unbind: function unbind (
    el,
    binding,
    vnode,
    oldVnode,
    isDestroy
  ) {
    if (!isDestroy) {
      el.style.display = el.__vOriginalDisplay;
    }
  }
}

var platformDirectives = {
  model: directive,
  show: show
}

/*  */

// Provides transition support for a single element/component.
// supports transition mode (out-in / in-out)
// 动画的props
var transitionProps = {
  name: String,
  appear: Boolean,
  css: Boolean,
  mode: String,
  type: String,
  enterClass: String,
  leaveClass: String,
  enterToClass: String,
  leaveToClass: String,
  enterActiveClass: String,
  leaveActiveClass: String,
  appearClass: String,
  appearActiveClass: String,
  appearToClass: String,
  duration: [Number, String, Object]
};

// in case the child is also an abstract component, e.g. <keep-alive>
// we want to recursively retrieve the real component to be rendered
// 获取子组件
function getRealChild (vnode) {
  var compOptions = vnode && vnode.componentOptions;
  if (compOptions && compOptions.Ctor.options.abstract) {
    return getRealChild(getFirstComponentChild(compOptions.children))
  } else {
    return vnode
  }
}

function extractTransitionData (comp) {
  var data = {};
  var options = comp.$options;
  // props
  for (var key in options.propsData) {
    data[key] = comp[key];
  }
  // events.
  // extract listeners and pass them directly to the transition methods
  var listeners = options._parentListeners;
  for (var key$1 in listeners) {
    data[camelize(key$1)] = listeners[key$1];
  }
  return data
}
// 是否是使用了缓存组件
function placeholder (h, rawChild) {
  if (/\d-keep-alive$/.test(rawChild.tag)) {
    return h('keep-alive', {
      props: rawChild.componentOptions.propsData
    })
  }
}
// 父组将是否有动画
function hasParentTransition (vnode) {
  while ((vnode = vnode.parent)) {
    if (vnode.data.transition) {
      return true
    }
  }
}
// child是否相同
function isSameChild (child, oldChild) {
  return oldChild.key === child.key && oldChild.tag === child.tag
}

var Transition = {
  name: 'transition',
  props: transitionProps,
  abstract: true,

  render: function render (h) {
    var this$1 = this;

    var children = this.$slots.default;
    if (!children) {
      return
    }

    // filter out text nodes (possible whitespaces)
    children = children.filter(function (c) { return c.tag || isAsyncPlaceholder(c); });
    /* istanbul ignore if */
    if (!children.length) {
      return
    }

    // warn multiple elements
    if ("development" !== 'production' && children.length > 1) {
      warn(
        '<transition> can only be used on a single element. Use ' +
        '<transition-group> for lists.',
        this.$parent
      );
    }

    var mode = this.mode;

    // warn invalid mode
    if ("development" !== 'production' &&
      mode && mode !== 'in-out' && mode !== 'out-in'
    ) {
      warn(
        'invalid <transition> mode: ' + mode,
        this.$parent
      );
    }

    var rawChild = children[0];

    // if this is a component root node and the component's
    // parent container node also has transition, skip.
    if (hasParentTransition(this.$vnode)) {
      return rawChild
    }

    // apply transition data to child
    // use getRealChild() to ignore abstract components e.g. keep-alive
    var child = getRealChild(rawChild);
    /* istanbul ignore if */
    if (!child) {
      return rawChild
    }

    if (this._leaving) {
      return placeholder(h, rawChild)
    }

    // ensure a key that is unique to the vnode type and to this transition
    // component instance. This key will be used to remove pending leaving nodes
    // during entering.
    var id = "__transition-" + (this._uid) + "-";
    child.key = child.key == null
      ? child.isComment
        ? id + 'comment'
        : id + child.tag
      : isPrimitive(child.key)
        ? (String(child.key).indexOf(id) === 0 ? child.key : id + child.key)
        : child.key;

    var data = (child.data || (child.data = {})).transition = extractTransitionData(this);
    var oldRawChild = this._vnode;
    var oldChild = getRealChild(oldRawChild);

    // mark v-show
    // so that the transition module can hand over the control to the directive
    if (child.data.directives && child.data.directives.some(function (d) { return d.name === 'show'; })) {
      child.data.show = true;
    }

    if (
      oldChild &&
      oldChild.data &&
      !isSameChild(child, oldChild) &&
      !isAsyncPlaceholder(oldChild) &&
      // #6687 component root is a comment node
      !(oldChild.componentInstance && oldChild.componentInstance._vnode.isComment)
    ) {
      // replace old child transition data with fresh one
      // important for dynamic transitions!
      var oldData = oldChild.data.transition = extend({}, data);
      // handle transition mode
      if (mode === 'out-in') {
        // return placeholder node and queue update when leave finishes
        this._leaving = true;
        mergeVNodeHook(oldData, 'afterLeave', function () {
          this$1._leaving = false;
          this$1.$forceUpdate();
        });
        return placeholder(h, rawChild)
      } else if (mode === 'in-out') {
        if (isAsyncPlaceholder(child)) {
          return oldRawChild
        }
        var delayedLeave;
        var performLeave = function () { delayedLeave(); };
        mergeVNodeHook(data, 'afterEnter', performLeave);
        mergeVNodeHook(data, 'enterCancelled', performLeave);
        mergeVNodeHook(oldData, 'delayLeave', function (leave) { delayedLeave = leave; });
      }
    }

    return rawChild
  }
}

/*  */

// Provides transition support for list items.
// supports move transitions using the FLIP technique.

// Because the vdom's children update algorithm is "unstable" - i.e.
// it doesn't guarantee the relative positioning of removed elements,
// we force transition-group to update its children into two passes:
// in the first pass, we remove all nodes that need to be removed,
// triggering their leaving transition; in the second pass, we insert/move
// into the final desired state. This way in the second pass removed
// nodes will remain where they should be.

var props = extend({
  tag: String,
  moveClass: String
}, transitionProps);

delete props.mode;
// transition-group 
var TransitionGroup = {
  props: props,

  render: function render (h) {
    var tag = this.tag || this.$vnode.data.tag || 'span';
    var map = Object.create(null);
    var prevChildren = this.prevChildren = this.children;
    var rawChildren = this.$slots.default || [];
    var children = this.children = [];
    var transitionData = extractTransitionData(this);

    for (var i = 0; i < rawChildren.length; i++) {
      var c = rawChildren[i];
      if (c.tag) {
        if (c.key != null && String(c.key).indexOf('__vlist') !== 0) {
          children.push(c);
          map[c.key] = c
          ;(c.data || (c.data = {})).transition = transitionData;
        } else {
          var opts = c.componentOptions;
          var name = opts ? (opts.Ctor.options.name || opts.tag || '') : c.tag;
          warn(("<transition-group> children must be keyed: <" + name + ">"));
        }
      }
    }

    if (prevChildren) {
      var kept = [];
      var removed = [];
      for (var i$1 = 0; i$1 < prevChildren.length; i$1++) {
        var c$1 = prevChildren[i$1];
        c$1.data.transition = transitionData;
        c$1.data.pos = c$1.elm.getBoundingClientRect();
        if (map[c$1.key]) {
          kept.push(c$1);
        } else {
          removed.push(c$1);
        }
      }
      this.kept = h(tag, null, kept);
      this.removed = removed;
    }

    return h(tag, null, children)
  },

  beforeUpdate: function beforeUpdate () {
    // force removing pass
    this.__patch__(
      this._vnode,
      this.kept,
      false, // hydrating
      true // removeOnly (!important, avoids unnecessary moves)
    );
    this._vnode = this.kept;
  },

  updated: function updated () {
    var children = this.prevChildren;
    var moveClass = this.moveClass || ((this.name || 'v') + '-move');
    if (!children.length || !this.hasMove(children[0].elm, moveClass)) {
      return
    }

    // we divide the work into three loops to avoid mixing DOM reads and writes
    // in each iteration - which helps prevent layout thrashing.
    children.forEach(callPendingCbs);
    children.forEach(recordPosition);
    children.forEach(applyTranslation);

    // force reflow to put everything in position
    // assign to this to avoid being removed in tree-shaking
    // $flow-disable-line
    this._reflow = document.body.offsetHeight;

    children.forEach(function (c) {
      if (c.data.moved) {
        var el = c.elm;
        var s = el.style;
        addTransitionClass(el, moveClass);
        s.transform = s.WebkitTransform = s.transitionDuration = '';
        el.addEventListener(transitionEndEvent, el._moveCb = function cb (e) {
          if (!e || /transform$/.test(e.propertyName)) {
            el.removeEventListener(transitionEndEvent, cb);
            el._moveCb = null;
            removeTransitionClass(el, moveClass);
          }
        });
      }
    });
  },

  methods: {
    hasMove: function hasMove (el, moveClass) {
      /* istanbul ignore if */
      if (!hasTransition) {
        return false
      }
      /* istanbul ignore if */
      if (this._hasMove) {
        return this._hasMove
      }
      // Detect whether an element with the move class applied has
      // CSS transitions. Since the element may be inside an entering
      // transition at this very moment, we make a clone of it and remove
      // all other transition classes applied to ensure only the move class
      // is applied.
      var clone = el.cloneNode();
      if (el._transitionClasses) {
        el._transitionClasses.forEach(function (cls) { removeClass(clone, cls); });
      }
      addClass(clone, moveClass);
      clone.style.display = 'none';
      this.$el.appendChild(clone);
      var info = getTransitionInfo(clone);
      this.$el.removeChild(clone);
      return (this._hasMove = info.hasTransform)
    }
  }
}