vue学习2

观察订阅模式

关于cleanupDeps函数

Watcher.prototype.cleanupDeps = function cleanupDeps () {
    var i = this.deps.length;
    while (i--) {
      var dep = this.deps[i];
      if (!this.newDepIds.has(dep.id)) {
        dep.removeSub(this);
      }
    }
    var tmp = this.depIds;
    this.depIds = this.newDepIds;
    this.newDepIds = tmp;
    this.newDepIds.clear();
    // 上面4行代码旧数据的删除     
    tmp = this.deps;
    this.deps = this.newDeps;
    this.newDeps = tmp;
    this.newDeps.length = 0;
    // 新数据的更新   
  };

该方法用于进行依赖dep的更新， 添加新的订阅移除旧的不需要的订阅。
比如 v-if 已不需要的模板依赖的数据发生变化时就不会通知watcher去 update， 当v-if模板不需要渲染时，它其中涉及到的数据不需要进行该watcher的订阅。
a.Watcher依赖收集的观察者
b.Dep依赖收集器 订阅者
c.Observe 类主要给响应式对象的属性添加 getter/setter 用于依赖收集与派发更新

生成虚拟DOM的render相关函数

function installRenderHelpers (target) {
    target._o = markOnce;
    target._n = toNumber;
    target._s = toString;
    target._l = renderList;
    target._t = renderSlot;
    target._q = looseEqual;
    target._i = looseIndexOf;
    target._m = renderStatic;
    target._f = resolveFilter;
    target._k = checkKeyCodes;
    target._b = bindObjectProps;
    target._v = createTextVNode;
    target._e = createEmptyVNode;
    target._u = resolveScopedSlots;
    target._g = bindObjectListeners;
    target._d = bindDynamicKeys;
    target._p = prependModifier;
  }

createFunctionalComponent函数式组件

a.组件的functional设置为true
b.组件提供一个render函数
c. render函数的返回结构类似 h(ele, attr, [children])

示例

Vue.component('my-transition', {
    functional:true,
    render:function (h, ctx) {
      var data = {
        props:{
          tag:'ul',
          css:false
        },
        on:{
          beforeEnter:function (el) {
            el.style.opacity = 0
            el.style.height = 0
          },
          enter:function (el, done) {
            var delay = el.dataset.index * 150
            setTimeout(function () {
              Velocity(el, {opacity:1, height:'1.6em'},{complete:done})
            }, delay)
          },
          leave:function (el, done) {
            var delay = el.dataset.index * 150
            setTimeout(function () {
              Velocity(el, {opacity:0, height:0}, {complete:done})
            }, delay)
          }
        }
      }
      return h('transition-group', data, ctx.children)
    },
    props:['query', 'list']
  })

component初始化钩子函数

// inline hooks to be invoked on component VNodes during patch
  var componentVNodeHooks = { 
    init: function init (node, hydrating) {},
    prepunch: function prepunch (oldVnode, Vnode) {},
    insert: function instert(vnode) {},
    destroy: function destroy(vnode) {}
}

初始化merge相关钩子函数
代码结构如下

installComponentHooks

组件创建的过程

createComponent方法的相关代码

…
// 继承自Vue
    if (isObject(Ctor)) {
          Ctor = baseCtor.extend(Ctor);
        }
…
    // 如果是异步组件
    asyncFactory = Ctor;
       Ctor = resolveAsyncComponent(asyncFactory, baseCtor, context);
…
    // resolve constructor options in case global mixins are applied after
       // component constructor creation
        resolveConstructorOptions(Ctor);
…
    // extract props
    var propsData = extractPropsFromVNodeData(data, Ctor, tag);
…
    // 如果是functional component
          return createFunctionalComponent(Ctor, propsData, data, context, children)
…
    // install component management hooks onto the placeholder node
        installComponentHooks(data);
…
    var vnode = new VNode(
      ("vue-component-" + (Ctor.cid) + (name ? ("-" + name) : '')),
      data, undefined, undefined, undefined, context,
      { Ctor: Ctor, propsData: propsData, listeners: listeners, tag: tag, children: children },
      asyncFactory
    );

    return vnode

v-model的实现

// transform component v-model info (value and callback) into
  // prop and event handler respectively.
  function transformModel (options, data) {
    var prop = (options.model && options.model.prop) || 'value';
    var event = (options.model && options.model.event) || 'input'
    ;(data.props || (data.props = {}))[prop] = data.model.value;
    var on = data.on || (data.on = {});
    var existing = on[event];
    var callback = data.model.callback;
    if (isDef(existing)) {
      if (
        Array.isArray(existing)
          ? existing.indexOf(callback) === -1
          : existing !== callback
      ) {
        on[event] = [callback].concat(existing);
      }
    } else {
      on[event] = callback;
    }
  }

有上面代码可知v-model会转换成prop 和event事件
示例1

<input v-model=“message” >
<input :value=“message” @input=“message=$event.target.value” >

可以通过设置model的属性 prop自定义变量 event来自定义属性
示例2

<my-msg v-model="testmsg"></my-msg>
Vue.component('my-msg', {
    template: `
      <div>
        <p>this is the value {{msg}}</p>
        <span @click="clickMe"> to click</span>
      </div>
    `,
    props: {
      msg: ''
    },
    model: {
      event: 'coustomEvent',
      prop: 'msg'
    },
    methods: {
      clickMe () {
        this.$emit('coustomEvent', this.msg + 'sss ')
      }
    }
  })

_createElement
_createElement构造虚拟DOM
_render函数
_render函数返回一个vnode
initMixin函数
initMixin函数包括Vue.prototype._init
其中_init执行Vue整个过程中涉及到的函数，实例化Vue的入口函数，其主要代码如下

// a flag to avoid this being observed
      vm._isVue = true;
      // merge 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
        );
      }
      /* istanbul ignore else */
      {
        initProxy(vm);
      }
      // expose real self
      vm._self = vm;
      initLifecycle(vm);
      initEvents(vm);
      initRender(vm);
      callHook(vm, 'beforeCreate');
      initInjections(vm); // resolve injections before data/props
      initState(vm);
      initProvide(vm); // resolve provide after data/props
      callHook(vm, 'created');

      /* istanbul ignore if */
      if (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);
      }

resolveConstructorOptions
resolveConstructorOptions处理options的相关属性

vue插件原理

initUse
initUse主要为vue挂载静态方法use， 其代码结构如下

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);
      // 将Vue对象注入       
      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
    };
  }

开发插件的示例代码

MyPlugin.install = function (Vue, options) {
  // 1. 添加全局方法或属性
  Vue.myGlobalMethod = function () {
    // 逻辑...
  }

  // 2. 添加全局资源
  Vue.directive('my-directive', {
    bind (el, binding, vnode, oldVnode) {
      // 逻辑...
    }
    ...
  })

  // 3. 注入组件
  Vue.mixin({
    created: function () {
      // 逻辑...
    }
    ...
  })

  // 4. 添加实例方法
  Vue.prototype.$myMethod = function (methodOptions) {
    // 逻辑...
  }
}

mixin

mixin的代码如下所示

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

由代码可知mixin将一些方法或属性挂载到 vue的静态options属性上
例如

Vue.mixin({
    created: function () {
      console.log('mixin created')
    }
  }) 

Vue继承

initExtend实现Vue的继承， 在组件初始化时创建一个继承自Vue的子对象
主要代码结构如下

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
}

pruneCache
删除keepAlive组件的缓存
其中keepAlive的生命周期函数还包括如下

var KeepAlive = { 
…
created (){},
destroyed () {},
mounted() {},
render() {}

}

initGlobalAPI
initGlobalAPI注册Vue的全局函数

renderClass
renderClass用来生成元素的class, 其中concat代码如下

function concat (a, b) {
    return a ? b ? (a + ' ' + b) : a : (b || '')
  }

其中涉及字符串化基本方法主要
stringifyClass、stringifyArray、stringifyObject

---

registerRef方法
registerRef方法用过注册设置ref属性的组件

自定义指令

自定义指令主要方法updateDirectives， 而该函数其实是对_update函数的调用
_update主要用来触发指令创建及变更指令中所涉及到的一些方法， 其代码结构如下

 function _update (oldVnode, vnode) {
    var isCreate = oldVnode === emptyNode;
    var isDestroy = vnode === emptyNode;
    var oldDirs = normalizeDirectives$1(oldVnode.data.directives, oldVnode.context);
    var newDirs = normalizeDirectives$1(vnode.data.directives, vnode.context);

    var dirsWithInsert = [];
    var dirsWithPostpatch = [];

    var key, oldDir, dir;
    for (key in newDirs) {
      oldDir = oldDirs[key];
      dir = newDirs[key];
      if (!oldDir) {
        // new directive, bind
        callHook$1(dir, 'bind', vnode, oldVnode);
        if (dir.def && dir.def.inserted) {
          dirsWithInsert.push(dir);
        }
      } else {
        // existing directive, update
        dir.oldValue = oldDir.value;
        dir.oldArg = oldDir.arg;
        callHook$1(dir, 'update', vnode, oldVnode);
        if (dir.def && dir.def.componentUpdated) {
          dirsWithPostpatch.push(dir);
        }
      }
    }

    if (dirsWithInsert.length) {
      var callInsert = function () {
        for (var i = 0; i < dirsWithInsert.length; i++) {
          callHook$1(dirsWithInsert[i], 'inserted', vnode, oldVnode);
        }
      };
      if (isCreate) {
        mergeVNodeHook(vnode, 'insert', callInsert);
      } else {
        callInsert();
      }
    }

    if (dirsWithPostpatch.length) {
      mergeVNodeHook(vnode, 'postpatch', function () {
        for (var i = 0; i < dirsWithPostpatch.length; i++) {
          callHook$1(dirsWithPostpatch[i], 'componentUpdated', vnode, oldVnode);
        }
      });
    }

    if (!isCreate) {
      for (key in oldDirs) {
        if (!newDirs[key]) {
          // no longer present, unbind
          callHook$1(oldDirs[key], 'unbind', oldVnode, oldVnode, isDestroy);
        }
      }
    }
  }

一个简单的例子如下

Vue.directive('mydir', {
    // 当被绑定的元素插入到 DOM 中时……
    inserted: function (el) {
      // 聚焦元素
      console.log('look my direct')
    }
  })

注意在模板编译的过程中会将指令名称转为小写，在创建指令时需采用小写方式

过滤器

parseFilters
parseFilters解析过滤器表达式
举个例子如下

Vue.filter('capitalize', function (value) {
    if (!value) return ''
    value = value.toString()
    return value.charAt(0).toUpperCase() + value.slice(1)
  })

{{message | capitalize}}

parseFilters返回的结果为"_f("capitalize")(message)"

编译过程

编译过程简单介绍
a.parser 将template模板生成抽象语法树
b.optimizer 对语法树进行优化处理，用来提升性能
c.codegen用来生成render函数

示例如下

<div>
  <header>
    <h1>I'm a template!</h1>
  </header>
  <p v-if="message">
    {{ message }}
  </p>
  <p v-else>
    No message.
  </p>

function anonymous() { with(this){return _c('div',[_m(0),(message)?_c('p',[_v(_s(message))]):_c('p',[_v("No message.")])])} }

vue动画过渡

组件或元素进入或离开时执行的动画过渡效果
a.组件为transition
b.条件渲染使用 v-if
c.条件展示 v-show
过渡钩子函数
1.v-enter过渡开始状态，元素被插入之前生效，在元素被插入的下一帧移除
2.v-enter-active定义过渡生效时的状态，在元素被插入之前生效动画完成之后移除
3.v-enter-to元素插入之后下一帧生效
4.v-leave离开时过渡开始时的状态
5.v-leave-active离开时过渡生效的状态，在过渡被触发是立即生效
6.v-leave-to离开过渡结束状态
元素插入时的钩子函数 为function enter (vnode, toggleDisplay)
定义v-show指令时，在bind， 和 update中会涉及 enter函数的调用, 可用v-show进行相关代码的调试
补充触发该动画时会进行_isMounted的判断, bind方法发生在mountComponent之前，如果设置默认变量为ture切不进行变更的情况下则不会触发动画函数
其中涉及到的动画进入代码代码主要如下

// 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);
            }
          }
        }
      });
    }

示例如下

<transition name="fade">
        <span v-show="isanimate" style="background: green; color: #fff">the animate</span>
 </transition>

.fade-enter-active, .fade-leave-active {
      transition: opacity 3s ease-out
    }
    .fade-enter, .fade-leave-to {
      opacity: 0;
    }

mounted () {
        console.log('to mounted')
        setTimeout(() => {
          this.isanimate = true
        }, 30)
      }

resolveTransition方法

macro task 和 micro task

其代码的执行顺序按照下列伪代码进行说明

for (macroTask of macroTaskQueue) {
   handleMacroTask()
   for (microTask of microTaskQueue) {
     handleMicroTask(microTask)
   }
 }

在浏览器中，常见的macro task任务有setTimeout MessageChannel postMessage setImmetiate
常见的micro task 有 MutationObserver 和Promise.then