Vue之Watcher源码解析（2）

// line-3846
  Vue.prototype._render = function() {

    // 获取参数

    try {
      // 死在这儿
      vnode = render.call(vm._renderProxy, vm.$createElement);
    } catch (e) {
      // 报render错误
    }
    // return empty vnode in case the render function errored out
    if (!(vnode instanceof VNode)) {
      // 返回空节点
    }
    // set parent
    vnode.parent = _parentVnode;
    return vnode
  };

// line-2374
  function mountComponent(vm, el, hydrating) {
    vm.$el = el;
    // error
    callHook(vm, 'beforeMount');

    var updateComponent;
    /* istanbul ignore if */
    if ("development" !== 'production' && config.performance && mark) {
      updateComponent = function() {
        // 开发者模式下的处理方式
      };
    } else {
      // 重新进入这里
      updateComponent = function() {
        vm._update(vm._render(), hydrating);
      };
    }

    vm._watcher = new Watcher(vm, updateComponent, noop);
    hydrating = false;

    // manually mounted instance, call mounted on self
    // mounted is called for render-created child components in its inserted hook
    if (vm.$vnode == null) {
      vm._isMounted = true;
      callHook(vm, 'mounted');
    }
    return vm
  }

// line-2374
  Vue.prototype._update = function(vnode, hydrating) {
    var vm = this;
    if (vm._isMounted) {
      callHook(vm, 'beforeUpdate');
    }
    // 保存原属性
    var prevEl = vm.$el;
    var prevVnode = vm._vnode;
    var prevActiveInstance = activeInstance;
    activeInstance = vm;
    vm._vnode = vnode;
    // patch
    if (!prevVnode) {
      // 初始化渲染
      vm.$el = vm.__patch__(
        vm.$el, vnode, hydrating, false /* removeOnly */ ,
        vm.$options._parentElm,
        vm.$options._refElm
      );
    } else {
      // 更新
      vm.$el = vm.__patch__(prevVnode, vnode);
    }
    activeInstance = prevActiveInstance;
    // update __vue__ reference
    if (prevEl) {
      prevEl.__vue__ = null;
    }
    if (vm.$el) {
      vm.$el.__vue__ = vm;
    }
    // if parent is an HOC, update its $el as well
    // HOC => High Order Component => 高阶组件
    if (vm.$vnode && vm.$parent && vm.$vnode === vm.$parent._vnode) {
      vm.$parent.$el = vm.$el;
    }
    // updated hook is called by the scheduler to ensure that children are
    // updated in a parent's updated hook.
  };

  // line-7526
  // install platform patch function
  Vue$3.prototype.__patch__ = inBrowser ? patch : noop;

  // line-6968
  var patch = createPatchFunction({
    nodeOps: nodeOps,
    modules: modules
  });

 // line-4762
  function createPatchFunction() {
    // fn1...
    // fn2...
    return function patch() {
      // 调用内部方法fn1,fn2...
    }
  }