Vue源码解读之InitState

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 && opts.watch !== nativeWatch) {
        initWatch(vm, opts.watch)
    }
}

function initProps(vm: Component, propsOptions: Object) {
    const propsData = vm.$options.propsData || {}
    const props = vm._props = {}
    const keys = vm.$options._propKeys = []
    const isRoot = !vm.$parent
    if (!isRoot) {
        toggleObserving(false)
    }
    for (const key in propsOptions) {
        keys.push(key)
        const value = validateProp(key, propsOptions, propsData, vm)
        defineReactive(props, key, value)
        if (!(key in vm)) {
            proxy(vm, `_props`, key)
        }
    }
    toggleObserving(true)
}

function proxy(target: Object, sourceKey: string, key: string) {
    sharedPropertyDefinition.get = function proxyGetter() {
        return this[sourceKey][key]
    }
    sharedPropertyDefinition.set = function proxySetter(val) {
        this[sourceKey][key] = val
    }
    Object.defineProperty(target, key, sharedPropertyDefinition)
}

function initMethods(vm: Component, methods: Object) {
    const props = vm.$options.props
    for (const key in methods) {
        if (process.env.NODE_ENV !== 'production') {
            if (typeof methods[key] !== 'function') {
                warn(`Method "${key}" has type "${typeof methods[key]}" in the component definition. ` + `Did you reference the function correctly?`, vm)
            }
            if (props && hasOwn(props, key)) {
                warn(`Method "${key}" has already been defined as a prop.`, vm)
            }
            if ((key in vm) && isReserved(key)) {
                warn(`Method "${key}" conflicts with an existing Vue instance method. ` + `Avoid defining component methods that start with _ or $.`)
            }
        }
        vm[key] = typeof methods[key] !== 'function' ? noop : bind(methods[key], vm)
    }
}

function initData(vm: Component) {
    let data = vm.$options.data
    data = vm._data = typeof data === 'function'
        ? getData(data, vm)
        : data || {}
    const keys = Object.keys(data)
    const props = vm.$options.props
    const methods = vm.$options.methods
    let i = keys.length
    while (i--) {
        const key = keys[i]
        if (process.env.NODE_ENV !== 'production') {
            if (methods && hasOwn(methods, key)) {
                warn(`Method "${key}" has already been defined as a data property.`, vm)
            }
        }
        if (props && hasOwn(props, key)) {
            process.env.NODE_ENV !== 'production' && warn(`The data property "${key}" is already declared as a prop. ` + `Use prop default value instead.`, vm)
        } else if (!isReserved(key)) {
            // 实现代理，可以this.massage 来进行访问this._data.message
            proxy(vm, `_data`, key)
        }
    }
    observe(data, true /* asRootData */)
}

function initComputed(vm: Component, computed: Object) {
    const watchers = vm._computedWatchers = Object.create(null)
    const isSSR = isServerRendering()

    for (const key in computed) {
        const userDef = computed[key]
        const getter = typeof userDef === 'function' ? userDef : userDef.get
        if (!isSSR) {
            watchers[key] = new Watcher(
                vm,
                getter || noop,
                noop,
                {
                    lazy: true
                }
            )
        }
        if (!(key in vm)) {
            defineComputed(vm, key, userDef)
        }
    }
}

function defineComputed(target: any, key: string, userDef: Object | Function) {
    const shouldCache = !isServerRendering()
    if (typeof userDef === 'function') {
        sharedPropertyDefinition.get = shouldCache
            ? createComputedGetter(key)
            : createGetterInvoker(userDef)
        sharedPropertyDefinition.set = noop
    } else {
        sharedPropertyDefinition.get = userDef.get
            ? shouldCache && userDef.cache !== false
                ? createComputedGetter(key)
                : createGetterInvoker(userDef.get)
            : noop
        sharedPropertyDefinition.set = userDef.set || noop
    }
    Object.defineProperty(target, key, sharedPropertyDefinition)
}

function createGetterInvoker(fn) {
    return function computedGetter() {
        return fn.call(this, this)
    }
}

function createComputedGetter(key) {
    return function computedGetter() {
        const watcher = this._computedWatchers && this._computedWatchers[key]
        if (watcher) {
            if (watcher.dirty) {
                watcher.evaluate()
            }
            if (Dep.target) {
                watcher.depend()
            }
            return watcher.value
        }
    }
}

function initWatch(vm: Component, watch: Object) {
    for (const key in watch) {
        const handler = watch[key]
        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, expOrFn: string | Function, handler: any, options?: Object) {
    if (isPlainObject(handler)) {
        options = handler
        handler = handler.handler
    }
    if (typeof handler === 'string') {
        handler = vm[handler]
    }
    return vm.$watch(expOrFn, handler, options)
}

watch: {
    telephone: function (newValue, oldValue) {
      console.log('telephone')
    },
    name: 'printName',
    message: ['printName', 'printValue'],
    address: [{
      handler: function (newValue, oldValue) {
        console.log('address')
      }
    }]
  },
  methods: {
    printName(newValue, oldValue) {
      console.log('printName')
    },
    printValue(newValue, oldValue) {
      console.log('printValue')
    }
  }

Vue.prototype.$watch = function (expOrFn: string | Function, cb: any, options?: Object): Function {
    const vm: Component = this
    if (isPlainObject(cb)) {
        return createWatcher(vm, expOrFn, cb, options)
    }
    options = options || {}
    options.user = true
    const watcher = new Watcher(vm, expOrFn, cb, options)
    if (options.immediate) {
        try {
            cb.call(vm, watcher.value)
        } catch (error) {
            handleError(error, vm, `callback for immediate watcher "${watcher.expression}"`)
        }
    }
    return function unwatchFn() {
        watcher.teardown()
    }
}