接下來看看lifecycleMixin方法，這個方法在Vue的原型上增加了_update、$forceUpdate和$destroy方法。
Vue.prototype._update = function (vnode, hydrating) {
var vm = this;
if (vm._isMounted) {
callHook(vm, 'beforeUpdate');
}
var prevEl = vm.$el;
var prevVnode = vm._vnode;
var prevActiveInstance = activeInstance;
activeInstance = vm;
vm._vnode = vnode;
// Vue.prototype.__patch__ is injected in entry points
// based on the rendering backend used.
if (!prevVnode) {
// initial render
vm.$el = vm.__patch__(
vm.$el, vnode, hydrating, false /* removeOnly */,
vm.$options._parentElm,
vm.$options._refElm
);
} else {
// updates
vm.$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 $el as well
if (vm.$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.
};_update是一個內部方法，首先判斷vue實例是否已經掛載，如果已掛載則調用callHook方法下發beforeUpdate事件。接下來進行了更新操作，主要是調用vm.__patch__方法進行更新。
Vue$3.prototype.__patch__ = inBrowser ? patch : noop如果在瀏覽器則爲patch方法，否則爲空函數。
var patch = createPatchFunction({ nodeOps: nodeOps, modules: modules });patch爲createPatchFunction函數創造的方法，傳入了一個對象。
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,
setAttribute: setAttribute
});nodeOps爲一個元素節點操作的對象，其中的方法是對原生的操作的一些封裝，而且這個對象爲freeze狀態，不可進行修改。
var modules = platformModules.concat(baseModules);
var platformModules = [
attrs,
klass,
events,
domProps,
style,
transition
];
var baseModules = [
ref,
directives
];modules爲兩個數組platformModules和baseModules合併而成，其中數組內都爲封裝的對象，每個對象有比如創建、更新等方法。
return function patch (oldVnode, vnode, hydrating, removeOnly, parentElm, refElm) {
if (isUndef(vnode)) {
if (isDef(oldVnode)) { invokeDestroyHook(oldVnode); }
return
}
var isInitialPatch = false;
var insertedVnodeQueue = [];
if (isUndef(oldVnode)) {
// empty mount (likely as component), create new root element
isInitialPatch = true;
createElm(vnode, insertedVnodeQueue, parentElm, refElm);
} else {
var isRealElement = isDef(oldVnode.nodeType);
if (!isRealElement && sameVnode(oldVnode, vnode)) {
// patch existing root node
patchVnode(oldVnode, vnode, insertedVnodeQueue, removeOnly);
} else {
if (isRealElement) {
// mounting to a real element
// check if this is server-rendered content and if we can perform
// a successful hydration.
if (oldVnode.nodeType === 1 && oldVnode.hasAttribute(SSR_ATTR)) {
oldVnode.removeAttribute(SSR_ATTR);
hydrating = true;
}
if (isTrue(hydrating)) {
if (hydrate(oldVnode, vnode, insertedVnodeQueue)) {
invokeInsertHook(vnode, insertedVnodeQueue, true);
return oldVnode
} else {
warn(
'The client-side rendered virtual DOM tree is not matching ' +
'server-rendered content. This is likely caused by incorrect ' +
'HTML markup, for example nesting block-level elements inside ' +
'<p>, or missing <tbody>. Bailing hydration and performing ' +
'full client-side render.'
);
}
}
// either not server-rendered, or hydration failed.
// create an empty node and replace it
oldVnode = emptyNodeAt(oldVnode);
}
// replacing existing element
var oldElm = oldVnode.elm;
var parentElm$1 = nodeOps.parentNode(oldElm);
createElm(
vnode,
insertedVnodeQueue,
// extremely rare edge case: do not insert if old element is in a
// leaving transition. Only happens when combining transition +
// keep-alive + HOCs. (#4590)
oldElm._leaveCb ? null : parentElm$1,
nodeOps.nextSibling(oldElm)
);
if (isDef(vnode.parent)) {
// component root element replaced.
// update parent placeholder node element, recursively
var ancestor = vnode.parent;
while (ancestor) {
ancestor.elm = vnode.elm;
ancestor = ancestor.parent;
}
if (isPatchable(vnode)) {
for (var i = 0; i < cbs.create.length; ++i) {
cbs.create[i](emptyNode, vnode.parent);
}
}
}
if (isDef(parentElm$1)) {
removeVnodes(parentElm$1, [oldVnode], 0, 0);
} else if (isDef(oldVnode.tag)) {
invokeDestroyHook(oldVnode);
}
}
}
invokeInsertHook(vnode, insertedVnodeQueue, isInitialPatch);
return vnode.elm
}createPatchFunction方法返回一個patch方法，這個方法涉及的內容較多，暫不分析。
Vue.prototype.$forceUpdate = function () {
var vm = this;
if (vm._watcher) {
vm._watcher.update();
}
};$forceUpdate方法主要是調用vue實例watcher的update方法更新。官方說明“它僅僅影響實例本身和插入插槽內容的子組件，而不是所有子組件”；目前在代碼裏沒有看出不更新其他子組件的原因。
Vue.prototype.$destroy = function () {
var vm = this;
if (vm._isBeingDestroyed) {
return
}
callHook(vm, 'beforeDestroy');
vm._isBeingDestroyed = true;
// remove self from parent
var parent = vm.$parent;
if (parent && !parent._isBeingDestroyed && !vm.$options.abstract) {
remove(parent.$children, vm);
}
// teardown watchers
if (vm._watcher) {
vm._watcher.teardown();
}
var i = vm._watchers.length;
while (i--) {
vm._watchers[i].teardown();
}
// remove reference from data ob
// frozen object may not have observer.
if (vm._data.__ob__) {
vm._data.__ob__.vmCount--;
}
// call the last hook...
vm._isDestroyed = true;
// invoke destroy hooks on current rendered tree
vm.__patch__(vm._vnode, null);
// fire destroyed hook
callHook(vm, 'destroyed');
// turn off all instance listeners.
vm.$off();
// remove __vue__ reference
if (vm.$el) {
vm.$el.__vue__ = null;
}
// remove reference to DOM nodes (prevents leak)
vm.$options._parentElm = vm.$options._refElm = null;
};$destroy方法主要做了幾件事情：
1、判斷vue實例是否已經銷燬；
2、調用callHook下發beforeDestroy事件；
3、移除實例中的子組件；
4、移除實例中的watchers；
5、將實例的vnode設爲空；
6、調用callHook下發destroyed事件；
7、調用vm.$off方法刪除所有綁定事件；
