一、Vue2.0的生命周期
Vue2.0的整个生命周期有八个：分别是 1.beforeCreate，2.created，3.beforeMount，4.mounted，5.beforeUpdate，6.updated，7.beforeDestroy，8.destroyed。
用官方的一张图就可以清晰的了解整个生命周期：
Vue最新源码下载：地址
二：源码分析
1.先看new Vue实例的方法
创建Vue实例的文件是: src/core/instance/index.js
function Vue (options) {
if (process.env.NODE_ENV !== 'production' &&
!(this instanceof Vue)) {
warn('Vue is a constructor and should be called with the `new` keyword')
}
this._init(options)
}
Vue的构造函数调用了this._init()方法，this._init()方法存在Vue的原型链中。在src/core/instance/init.js文件中：
export function initMixin (Vue: Class<Component>) {
Vue.prototype._init = function (options?: Object) {
const vm: Component = this
// a uid
vm._uid = uid++
// a flag to avoid this being observed
vm._isVue = true
// merge options 第一步： options参数的处理
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.$options = mergeOptions(
resolveConstructorOptions(vm.constructor),
options || {},
vm
)
}
/* istanbul ignore else 第二步：renderProxy */
if (process.env.NODE_ENV !== 'production') {
initProxy(vm)
} else {
vm._renderProxy = vm
}
// expose real self
vm._self = vm
// 第三步：vm的生命周期相关变量初始化
initLifecycle(vm)
// 第四步：vm的事件监听初始化
initEvents(vm)
// 第五步： render
initRender(vm)
callHook(vm, 'beforeCreate')
// 第六步：vm的状态初始化，prop/data/computed/method/watch都在这里完成初始化
initState(vm)
callHook(vm, 'created')
if (vm.$options.el) {
vm.$mount(vm.$options.el)
}
}
}
接下来继续分析每一步的详细实现。
第一步： options参数的处理
// merge options 第一步： options参数的处理
if (options && options._isComponent) {
// optimize internal component instantiation 优化内部组件实例
// since dynamic options merging is pretty slow, and none of the 因为动态options融合比较慢，而内部组件options不需要特别处理
// internal component options needs special treatment.
initInternalComponent(vm, options)
} else {
vm.$options = mergeOptions(
resolveConstructorOptions(vm.constructor),
options || {},
vm
)
}
initInternalComponent的方法为：
function initInternalComponent (vm: Component, options: InternalComponentOptions) {
const opts = vm.$options = Object.create(vm.constructor.options)
// doing this because it's faster than dynamic enumeration. 做这些是因为它比动态计数要快
opts.parent = options.parent
opts.propsData = options.propsData
opts._parentVnode = options._parentVnode
opts._parentListeners = options._parentListeners
opts._renderChildren = options._renderChildren
opts._componentTag = options._componentTag
opts._parentElm = options._parentElm
opts._refElm = options._refElm
if (options.render) {
opts.render = options.render
opts.staticRenderFns = options.staticRenderFns
}
}
Vue是一套组件化系统，子组件的options必然受到父组件的影响、即使是同一个组件，我们也有公用的options（挂载在构造器上）和差异的options（实例传入的options），因此处理options时我们要处理四个相关的options：
- 父组件构造器上的options
- 父组件实例上的options
- 当前组件构造器上的options
- 当前组件实例化传入的options
vm.$options = mergeOptions(
resolveConstructorOptions(vm.constructor),
options || {},
vm
)
resolveConstructorOptions的方法为：
export function resolveConstructorOptions (Ctor: Class<Component>) {
let options = Ctor.options
if (Ctor.super) { // 如果有父级
const superOptions = Ctor.super.options // 获取父级的options
const cachedSuperOptions = Ctor.superOptions // 获取父级缓存的options
const extendOptions = Ctor.extendOptions // 获取自身的options
if (superOptions !== cachedSuperOptions) { // 如果父级options有变化
// super option changed
Ctor.superOptions = superOptions // 更新缓存
extendOptions.render = options.render
extendOptions.staticRenderFns = options.staticRenderFns
extendOptions._scopeId = options._scopeId
options = Ctor.options = mergeOptions(superOptions, extendOptions)
if (options.name) {
options.components[options.name] = Ctor
}
}
}
return options
}
接下来就重点看mergeOptions（文件位置在src\core\util\options.js）的实现了：
/**
* Merge two option objects into a new one. 将两个参数融合成一个
* Core utility used in both instantiation and inheritance. 核心公用的会被用于实例和继承中
*/
export function mergeOptions (
parent: Object,
child: Object,
vm?: Component
): Object {
if (process.env.NODE_ENV !== 'production') {
checkComponents(child)
}
// 统一props格式
normalizeProps(child)
// 统一directives的格式
normalizeDirectives(child)
const extendsFrom = child.extends
// 如果存在child.extends
if (extendsFrom) {
parent = typeof extendsFrom === 'function'
? mergeOptions(parent, extendsFrom.options, vm)
: mergeOptions(parent, extendsFrom, vm) // 递归调用该方法
}
if (child.mixins) {
//如果存在child.mixins
for (let i = 0, l = child.mixins.length; i < l; i++) {
let mixin = child.mixins[i]
if (mixin.prototype instanceof Vue) {
mixin = mixin.options
}
parent = mergeOptions(parent, mixin, vm)
}
}
//针对不同的键值，采用不同的merge策略
const options = {}
let key
for (key in parent) {
mergeField(key)
}
for (key in child) {
if (!hasOwn(parent, key)) {
mergeField(key)
}
}
function mergeField (key) {
const strat = strats[key] || defaultStrat
options[key] = strat(parent[key], child[key], vm, key)
}
return options
}
上面采取了对不同的field采取不同的策略，Vue提供了一个strats对象，其本身就是一个hook,如果strats有提供特殊的逻辑，就走strats,否则走默认merge逻辑。
/**
* Option overwriting strategies are functions that handle
* how to merge a parent option value and a child option
* value into the final value.
*/
const strats = config.optionMergeStrategies
第二步：renderProxy
主要是定义了vm._renderProxy，这是后期为render做准备的
/* istanbul ignore else 第二步：renderProxy */
if (process.env.NODE_ENV !== 'production') {
initProxy(vm)
} else {
vm._renderProxy = vm
}
作用是在render中将this指向vm._renderProxy。一般而言，vm._renderProxy是等于vm的，但在开发环境，Vue动用了Proxy这个新API
看下initProxy（存放于src\core\instance\proxy.js） 这个方法
initProxy = function initProxy (vm) {
if (hasProxy) {
// determine which proxy handler to use 确定用哪个proxy handler
const options = vm.$options
const handlers = options.render && options.render._withStripped
? getHandler
: hasHandler // getHandler和hasHandler在上面有定义
vm._renderProxy = new Proxy(vm, handlers)
} else {
vm._renderProxy = vm
}
}
Proxy 学习资源
ES6规范定义了一个全新的全局构造函数：代理（Proxy）。它可以接受两个参数：目标对象（vm）和句柄对象（handlers）。
一个简单示例：
var target = {}, handler = {};
var proxy = new Proxy(target, handler);
1.代理和目标对象之间的关系：
代理的行为很简单：将代理的所有内部方法转发至目标。简单来说，如果调用proxy.[[Enumerate]]()，就会返回target.[[Enumerate]]()。
现在，让我们尝试执行一条能够触发调用proxy.[[Set]]()方法的语句。
此时target的结果看看
2.代理和句柄对象的关系：
句柄对象的方法可以覆写任意代理的内部方法。举个例子，定义一个handler.set()方法来拦截所有给对象属性赋值的行为：
var target = {};
var handler = {
set: function (target, key, value, receiver) {
throw new Error("请不要为这个对象设置属性。");
}
};
var proxy = new Proxy(target, handler);
结果：
第三步：vm的生命周期相关变量初始化
// 第三步：vm的生命周期相关变量初始化
initLifecycle(vm)
initLifecycle该方法存在于src\core\instance\lifecycle.js文件中
export function initLifecycle (vm: Component) {
const options = vm.$options
// locate first non-abstract parent
let parent = options.parent
if (parent && !options.abstract) {
while (parent.$options.abstract && parent.$parent) {
parent = parent.$parent
}
parent.$children.push(vm)
}
vm.$parent = parent
vm.$root = parent ? parent.$root : vm
vm.$children = []
vm.$refs = {}
vm._watcher = null
vm._inactive = false
vm._isMounted = false
vm._isDestroyed = false
vm._isBeingDestroyed = false
}
第四步：vm的事件监听初始化
// 第四步：vm的事件监听初始化
initEvents(vm)
initEvents方法存在于src\core\instance\event.js中
export function initEvents (vm: Component) {
vm._events = Object.create(null)
vm._hasHookEvent = false
// init parent attached events
const listeners = vm.$options._parentListeners
if (listeners) {
updateComponentListeners(vm, listeners)
}
}
export function updateComponentListeners (
vm: Component,
listeners: Object,
oldListeners: ?Object
) {
target = vm
updateListeners(listeners, oldListeners || {}, add, remove, vm)
}
updateListeners方法存在于src\core\vdom\helper\update-listeners.js
export function updateListeners (
on: Object,
oldOn: Object,
add: Function,
remove: Function,
vm: Component
) {
let name, cur, old, event
for (name in on) {
cur = on[name]
old = oldOn[name]
event = normalizeEvent(name)
if (!cur) {
process.env.NODE_ENV !== 'production' && warn(
`Invalid handler for event "${event.name}": got ` + String(cur),
vm
)
} else if (!old) {
// 新添加的listener
if (!cur.invoker) {
cur = on[name] = createEventHandle(cur)
}
add(event.name, cur.invoker, event.once, event.capture)
} else if (cur !== old) {
// 替换旧的事件监听
old.fn = cur
on[name] = old
}
}
// 删除无用的listeners
for (name in oldOn) {
if (!on[name]) {
event = normalizeEvent(name)
remove(event.name, oldOn[name].invoker, event.capture)
}
}
}
第五步： render
// 第五步： render
initRender(vm)
initRender存放于src\core\instance\render.js
export function initRender (vm: Component) {
vm.$vnode = null // the placeholder node in parent tree 在父级树上的提示节点？
vm._vnode = null // the root of the child tree 子级的根节点
vm._staticTrees = null
const parentVnode = vm.$options._parentVnode
const renderContext = parentVnode && parentVnode.context
vm.$slots = resolveSlots(vm.$options._renderChildren, renderContext)
vm.$scopedSlots = emptyObject
// bind the createElement fn to this instance 绑定创建元素到这个实例
// so that we get proper render context inside it. 以方便我们能获得正确的渲染内容
// args order: tag, data, children, normalizationType, alwaysNormalize 参数提供： tag,data, children,normalizationType,alwaysNormalize
// internal version is used by render functions compiled from templates 内部版本用来编译从templates来的函数？
vm._c = (a, b, c, d) => createElement(vm, a, b, c, d, false) // 箭头函数，相当于function(a,b,c,d) { return createElement(vm, a, b, c, d, false) }
// normalization is always applied for the public version, used in
// user-written render functions. 统一化？
vm.$createElement = (a, b, c, d) => createElement(vm, a, b, c, d, true)
}
createElement方法存放于src\core\vdom\create-element.js
// wrapper function for providing a more flexible interface 封装方法用来提供一个可扩展性的接口
// without getting yelled at by flow 不是流程式
export function createElement (
context: Component,
tag: any,
data: any,
children: any,
normalizationType: any,
alwaysNormalize: boolean
): VNode {
if (Array.isArray(data) || isPrimitive(data)) {
normalizationType = children
children = data
data = undefined
}
if (alwaysNormalize) normalizationType = ALWAYS_NORMALIZE
return _createElement(context, tag, data, children, normalizationType)
}
_createElement方法也在这个文件中
export function _createElement (
context: Component,
tag?: string | Class<Component> | Function | Object,
data?: VNodeData,
children?: any,
normalizationType?: number
): VNode {
if (data && data.__ob__) {
process.env.NODE_ENV !== 'production' && warn(
`Avoid using observed data object as vnode data: ${JSON.stringify(data)}\n` +
'Always create fresh vnode data objects in each render!',
context
)
return createEmptyVNode()
}
if (!tag) {
// in case of component :is set to falsy value
return createEmptyVNode()
}
// support single function children as default scoped slot
if (Array.isArray(children) &&
typeof children[0] === 'function') {
data = data || {}
data.scopedSlots = { default: children[0] }
children.length = 0
}
if (normalizationType === ALWAYS_NORMALIZE) {
children = normalizeChildren(children)
} else if (normalizationType === SIMPLE_NORMALIZE) {
children = simpleNormalizeChildren(children)
}
let vnode, ns
if (typeof tag === 'string') {
let Ctor
ns = config.getTagNamespace(tag)
if (config.isReservedTag(tag)) {
// platform built-in elements
vnode = new VNode(
config.parsePlatformTagName(tag), data, children,
undefined, undefined, context
)
} else if ((Ctor = resolveAsset(context.$options, 'components', tag))) {
// component
vnode = createComponent(Ctor, data, context, children, tag)
} else {
// unknown or unlisted namespaced elements
// check at runtime because it may get assigned a namespace when its
// parent normalizes children
vnode = new VNode(
tag, data, children,
undefined, undefined, context
)
}
} else {
// direct component options / constructor
vnode = createComponent(tag, data, context, children)
}
if (vnode) {
if (ns) applyNS(vnode, ns)
return vnode
} else {
return createEmptyVNode()
}
}
文件中引用了VNode这个类和createEmptyVNode方法，这两个东西存放于src\core\vdom\vnode.js
export default class VNode {
tag: string | void;
data: VNodeData | void;
children: ?Array<VNode>;
text: string | void;
elm: Node | void;
ns: string | void;
context: Component | void; // rendered in this component's scope
functionalContext: Component | void; // only for functional component root nodes
key: string | number | void;
componentOptions: VNodeComponentOptions | void;
componentInstance: Component | void; // component instance
parent: VNode | void; // component placeholder node
raw: boolean; // contains raw HTML? (server only)
isStatic: boolean; // hoisted static node
isRootInsert: boolean; // necessary for enter transition check
isComment: boolean; // empty comment placeholder?
isCloned: boolean; // is a cloned node?
isOnce: boolean; // is a v-once node?
constructor (
tag?: string,
data?: VNodeData,
children?: ?Array<VNode>,
text?: string,
elm?: Node,
context?: Component,
componentOptions?: VNodeComponentOptions
) {
this.tag = tag
this.data = data
this.children = children
this.text = text
this.elm = elm
this.ns = undefined
this.context = context
this.functionalContext = undefined
this.key = data && data.key
this.componentOptions = componentOptions
this.componentInstance = undefined
this.parent = undefined
this.raw = false
this.isStatic = false
this.isRootInsert = true
this.isComment = false
this.isCloned = false
this.isOnce = false
}
// DEPRECATED: alias for componentInstance for backwards compat.
/* istanbul ignore next */
get child (): Component | void {
return this.componentInstance
}
}
createEmptyVNode方法
export const createEmptyVNode = () => {
const node = new VNode()
node.text = ''
node.isComment = true
return node
}
第六步：vm的状态初始化，prop/data/computed/method/watch都在这里完成初始化
// 第六步：vm的状态初始化，prop/data/computed/method/watch都在这里完成初始化
initState(vm)
initState存放于src\core\instance\state.js
export function initState (vm: Component) {
vm._watchers = []
const opts = vm.$options
if (opts.props) initProps(vm, opts.props)
if (opts.methods) initMethods(vm, opts.methods)
if (opts.data) {
initData(vm)
} else {
observe(vm._data = {}, true /* asRootData */)
}
if (opts.computed) initComputed(vm, opts.computed)
if (opts.watch) initWatch(vm, opts.watch)
}
vm的状态初始化是整个初始化中最复杂的异步，其data、props、methods、computed、watch都在这一步进行初始化，因此这一步也是Vue真正的创建。
initProps
function initProps (vm: Component, propsOptions: Object) {
const propsData = vm.$options.propsData || {}
const props = vm._props = {}
// cache prop keys so that future props updates can iterate using Array
// instead of dynamic object key enumeration.
const keys = vm.$options._propKeys = []
const isRoot = !vm.$parent
// root instance props should be converted
observerState.shouldConvert = isRoot
for (const key in propsOptions) {
keys.push(key)
const value = validateProp(key, propsOptions, propsData, vm)
/* istanbul ignore else */
if (process.env.NODE_ENV !== 'production') {
if (isReservedProp[key]) {
warn(
`"${key}" is a reserved attribute and cannot be used as component prop.`,
vm
)
}
defineReactive(props, key, value, () => { // 监控prop的变化
if (vm.$parent && !observerState.isSettingProps) {
warn(
`Avoid mutating a prop directly since the value will be ` +
`overwritten whenever the parent component re-renders. ` +
`Instead, use a data or computed property based on the prop's ` +
`value. Prop being mutated: "${key}"`,
vm
)
}
})
} else {
defineReactive(props, key, value)
}
// static props are already proxied on the component's prototype
// during Vue.extend(). We only need to proxy props defined at
// instantiation here.
if (!(key in vm)) {
proxy(vm, `_props`, key)
}
}
observerState.shouldConvert = true
}
initMethods
function initMethods (vm: Component, methods: Object) {
for (const key in methods) {
vm[key] = methods[key] == null ? noop : bind(methods[key], vm) // 作用域重新绑定
if (process.env.NODE_ENV !== 'production' && methods[key] == null) {
warn(
`method "${key}" has an undefined value in the component definition. ` +
`Did you reference the function correctly?`,
vm
)
}
}
}
initData
function initData (vm: Component) {
let data = vm.$options.data
data = vm._data = typeof data === 'function'
? data.call(vm)
: data || {}
if (!isPlainObject(data)) {
// 保证data必须为纯对象
data = {}
process.env.NODE_ENV !== 'production' && warn(
'data functions should return an object:\n' +
'https://vuejs.org/v2/guide/components.html#data-Must-Be-a-Function',
vm
)
}
// proxy data on instance
const keys = Object.keys(data)
const props = vm.$options.props
let i = keys.length
while (i--) {
if (props && hasOwn(props, keys[i])) {
process.env.NODE_ENV !== 'production' && warn(
`The data property "${keys[i]}" is already declared as a prop. ` +
`Use prop default value instead.`,
vm
)
} else if (!isReserved(keys[i])) {
proxy(vm, `_data`, keys[i]) //将属性代理到vm上
}
}
// observe data 将data转换为监控对象
observe(data, true /* asRootData */)
}
initComputed
const computedWatcherOptions = { lazy: true }
function initComputed (vm: Component, computed: Object) {
const watchers = vm._computedWatchers = Object.create(null)
for (const key in computed) {
const userDef = computed[key]
const getter = typeof userDef === 'function' ? userDef : userDef.get
// create internal watcher for the computed property.
watchers[key] = new Watcher(vm, getter, noop, computedWatcherOptions)
// component-defined computed properties are already defined on the
// component prototype. We only need to define computed properties defined
// at instantiation here.
if (!(key in vm)) {
defineComputed(vm, key, userDef)
}
}
}
export function defineComputed (target: any, key: string, userDef: Object | Function) {
if (typeof userDef === 'function') {
sharedPropertyDefinition.get = createComputedGetter(key)
sharedPropertyDefinition.set = noop
} else {
sharedPropertyDefinition.get = userDef.get
? userDef.cache !== false
? createComputedGetter(key)
: userDef.get
: noop
sharedPropertyDefinition.set = userDef.set
? userDef.set
: noop
}
Object.defineProperty(target, key, sharedPropertyDefinition)
}
computed其实本身也是一种特殊的并且lazy的watcher,在get时它作为所计算的属性依赖而被收集，同时它把依赖自己的watcher也添加到属性的依赖中去，这样当原属性变化时，就会通知到依赖computed的依赖重新获取最新值。
function createComputedGetter (key) {
return function computedGetter () {
const watcher = this._computedWatchers && this._computedWatchers[key]
if (watcher) {
if (watcher.dirty) {
// 将自己添加到属性的依赖列表中去
watcher.evaluate()
}
if (Dep.target) {
// 将依赖watcher的依赖也收集到属性依赖列表中去
watcher.depend()
}
return watcher.value
}
}
}
initWatch
function initWatch (vm: Component, watch: Object) {
for (const key in watch) {
const handler = watch[key]
// 可以是数组，为key创建多个watcher
if (Array.isArray(handler)) {
for (let i = 0; i < handler.length; i++) {
createWatcher(vm, key, handler[i])
}
} else {
createWatcher(vm, key, handler)
}
}
}
function createWatcher (vm: Component, key: string, handler: any) {
let options
if (isPlainObject(handler)) {
options = handler
handler = handler.handler
}
// 如果handle传入为字符串，则直接找vm上的方法，一般是methods中定义的方法，这也是methods的初始化要先于watch初始化的原因
if (typeof handler === 'string') {
handler = vm[handler]
}
vm.$watch(key, handler, options) // 没找到$watch在原型上的定义
}
经过这些初始化的步骤，一个组件就被创造出来了，紧接着就可以callHook(vm, 'created')。
至此，我们主要了解了Vue整个生命周期，以及Vue创建（created）前的过程，从生命周期图中可以看到还有重要一步 Observe Data没有分析，状态初始化过程中用到监控对象如observe(data)，依赖收集Dep等等，分析完Observe Data 应该就可以了解到Vue的数据绑定原理，这个分析留给下一篇文章。
参考资料：http://blog.cgsdream.org/2016/11/11/vue-source-analysis-2/