先來個流程圖，水平有限，炊訓看吧-_-||
首先在創建一個Vue應用時：
var app = new Vue({ el: '#app', data: { message: 'Hello Vue!' } })
Vue建構式原始碼：
//創建Vue建構式 function Vue (options) { if (!(this instanceof Vue) ) { warn('Vue is a constructor and should be called with the `new` keyword'); } this._init(options); } //_init方法，會初始化data,watch,computed等 Vue.prototype._init = function (options) { var vm = this; // a uid vm._uid = uid$3++; ...... // expose real self vm._self = vm; initLifecycle(vm); initEvents(vm); initRender(vm); callHook(vm, 'beforeCreate'); initInjections(vm); // resolve injections before data/props initState(vm); ...... };
在initState方法中會初始化data、watch和computed，并呼叫observe函式監聽data(Object.defineProperty)：
function initState (vm) { vm._watchers = []; var opts = vm.$options; if (opts.props) { initProps(vm, opts.props); } if (opts.methods) { initMethods(vm, opts.methods); } if (opts.data) { initData(vm);//initData中也會呼叫observe方法 } else { observe(vm._data = {}, true /* asRootData */); } if (opts.computed) { initComputed(vm, opts.computed); } if (opts.watch && opts.watch !== nativeWatch) { initWatch(vm, opts.watch); } }
1、observe
observe在initState 時被呼叫，為vue實體的data屬性值創建getter、setter函式，在setter中dep.depend會把watcher實體添加到Dep實體的subs屬性中，在getter中會呼叫dep.notify，呼叫watcher的update方法，
/**
* Attempt to create an observer instance for a value,
* returns the new observer if successfully observed,
* or the existing observer if the value already has one.
* 該函式在initState中有呼叫
*/
function observe (value, asRootData) {
if (!isObject(value) || value instanceof VNode) {
return
}
var ob;
if (hasOwn(value, '__ob__') && value.__ob__ instanceof Observer) {
ob = value.__ob__;
} else if (
shouldObserve &&
!isServerRendering() &&
(Array.isArray(value) || isPlainObject(value)) &&
Object.isExtensible(value) &&
!value._isVue
) {
ob = new Observer(value);
}
if (asRootData && ob) {
ob.vmCount++;
}
re * Observer class that is attached to each observed
* object. Once attached, the observer converts the target * object's property keys into getter/setters that * collect dependencies and dispatch updates. */ var Observer = function Observer (value) { this.value =https://www.cnblogs.com/gxp69/p/ value; this.dep = new Dep(); this.vmCount = 0; def(value, '__ob__', this); if (Array.isArray(value)) { if (hasProto) { protoAugment(value, arrayMethods); } else { copyAugment(value, arrayMethods, arrayKeys); } this.observeArray(value); } else { this.walk(value); } }; /** * Walk through all properties and convert them into * getter/setters. This method should only be called when * value type is Object. */ Observer.prototype.walk = function walk (obj) { var keys = Object.keys(obj); for (var i = 0; i < keys.length; i++) { defineReactive$$1(obj, keys[i]); } }; /** * Define a reactive property on an Object. */ function defineReactive$$1 ( obj, key, val, customSetter, shallow ) { var dep = new Dep(); var property = Object.getOwnPropertyDescriptor(obj, key); if (property && property.configurable === false) { return } // cater for pre-defined getter/setters var getter = property && property.get; var setter = property && property.set; if ((!getter || setter) && arguments.length === 2) { val = obj[key]; } var childOb = !shallow && observe(val); Object.defineProperty(obj, key, { enumerable: true, configurable: true, get: function reactiveGetter () { var value = https://www.cnblogs.com/gxp69/p/getter ? getter.call(obj) : val;
//Dep.target 全域變數指向的就是指向當前正在決議生成的 Watcher
//會執行到dep.addSub，將Watcher添加到Dep物件的Watcher陣列中 if (Dep.target) { dep.depend(); if (childOb) { childOb.dep.depend(); if (Array.isArray(value)) { dependArray(value); } } } return value }, set: function reactiveSetter (newVal) { var value = https://www.cnblogs.com/gxp69/p/getter ? getter.call(obj) : val; /* eslint-disable no-self-compare */ if (newVal === value || (newVal !== newVal && value !== value)) { return } /* eslint-enable no-self-compare */ if (customSetter) { customSetter(); } // #7981: for accessor properties without setter if (getter && !setter) { return } if (setter) { setter.call(obj, newVal); } else { val = newVal; } childOb = !shallow && observe(newVal); dep.notify();//如果資料被重新賦值了, 呼叫 Dep 的 notify 方法, 通知所有的 Watcher
} }); }
2、Dep
Watcher的update方法是在new Dep的notify的方法中被呼叫的
/**
* A dep is an observable that can have multiple
* directives subscribing to it.
*/
var Dep = function Dep () {
this.id = uid++;
this.subs = [];
};
//設定某個Watcher的依賴
//這里添加Dep.target，用來判斷是不是Watcher的建構式呼叫
//也就是其this.get呼叫
Dep.prototype.depend = function depend () {
if (Dep.target) {
Dep.target.addDep(this);
}
};
//在該方法中會觸發subs的update方法
Dep.prototype.notify = function notify () {
// stabilize the subscriber list first
var subs = this.subs.slice();
if (!config.async) {
// subs aren't sorted in scheduler if not running async
// we need to sort them now to make sure they fire in correct
// order
subs.sort(function (a, b) { return a.id - b.id; });
}
for (var i = 0, l = subs.length; i < l; i++) {
subs[i].update();
}
};
3、watch
初始化watch，函式中會呼叫createWatcher，createWatcher會呼叫$watch，$watch呼叫new Watcher實體，
function initWatch (vm, watch) { for (var key in watch) { var handler = watch[key]; if (Array.isArray(handler)) { for (var i = 0; i < handler.length; i++) { createWatcher(vm, key, handler[i]); } } else { createWatcher(vm, key, handler); } } } function createWatcher ( vm, expOrFn, handler, options ) { if (isPlainObject(handler)) { options = handler; handler = handler.handler; } if (typeof handler === 'string') { handler = vm[handler]; } return vm.$watch(expOrFn, handler, options) } Vue.prototype.$watch = function ( expOrFn, cb, options ) { var vm = this; if (isPlainObject(cb)) { return createWatcher(vm, expOrFn, cb, options) } options = options || {}; options.user = true; var 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(); } }; }
2、computed
初始化computed，呼叫new Watcher()，并通過defineComputed函式將計算屬性掛載到vue實體上，使計算屬性可以在模板中使用
var computedWatcherOptions = { lazy: true }
function initComputed (vm, computed) { // $flow-disable-line var watchers = vm._computedWatchers = Object.create(null); // computed properties are just getters during SSR var isSSR = isServerRendering(); for (var key in computed) { var userDef = computed[key]; var getter = typeof userDef === 'function' ? userDef : userDef.get;
//getter也就是computed的函式 if (getter == null) { warn( ("Getter is missing for computed property \"" + key + "\"."), vm ); } if (!isSSR) { // create internal watcher for the computed property. watchers[key] = new Watcher( vm, getter || noop, noop, computedWatcherOptions ); } //組件定義的計算屬性已在 //組件原型，我們只需要定義定義的計算屬性 //在這里實體化， if (!(key in vm)) { defineComputed(vm, key, userDef); } else { if (key in vm.$data) { warn(("The computed property \"" + key + "\" is already defined in data."), vm); } else if (vm.$options.props && key in vm.$options.props) { warn(("The computed property \"" + key + "\" is already defined as a prop."), vm); } } } }
function defineComputed (
target,
key,
userDef
) {
var shouldCache = !isServerRendering();//true
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;
}
if (sharedPropertyDefinition.set === noop) {
sharedPropertyDefinition.set = function () {
warn(
("Computed property \"" + key + "\" was assigned to but it has no setter."),
this
);
};
}
Object.defineProperty(target, key, sharedPropertyDefinition);
}
//computed的getter函式，在模板獲取對應computed資料時會呼叫
function createComputedGetter (key) {
return function computedGetter () {
var watcher = this._computedWatchers && this._computedWatchers[key];
if (watcher) {
if (watcher.dirty) {//true
watcher.evaluate();//該方法會呼叫watcher.get方法，也就是computed對應的函式
}
if (Dep.target) {
watcher.depend();
}
return watcher.value
}
}
}
通過以上代碼可以看到watch和computed都是通過new Watcher實體實作資料的監聽的，但是computed的options中lazy為true，這個引數導致它們走的是兩條不同路線，
computed：模板獲取資料時，觸發其getter函式，最終呼叫watcher.get，也就是呼叫對應回呼函式，
watch：模板獲取資料時，觸發其getter函式，將watcher添加到對應的Dep.subs中，在之后setter被呼叫時，Dep.notify通知所有watcher進行update，最終呼叫watcher.cb,也就是呼叫對應回呼函式，
3、Watcher
建構式在是watch時，會最后呼叫this.get，會觸發屬性的getter函式，將該Watcher添加到Dep的subs中，用于通知資料變動時呼叫，
呼叫Watcher實體的update方法會觸發其run方法，run方法中會呼叫觸發函式，其depend方法會呼叫new Dep的depend方法，dep的depend會呼叫Watcher的addDep方法，最侄訓把該watcher實體添加到Dep的subs屬性中
/** *觀察者決議運算式，收集依賴項， *并在運算式值更改時激發回呼， *這用于$watch（）api和指令， */ var Watcher = function Watcher ( vm, expOrFn, cb, options, isRenderWatcher ) { this.vm = vm; ...... this.cb = cb;//觸發函式 this.id = ++uid$2; // uid for batching this.active = true; this.dirty = this.lazy; // for lazy watchers ...... this.value = https://www.cnblogs.com/gxp69/p/this.lazy ? undefined ? this.get();//computed會回傳undefined，而watch會執行Watcher.get }; /** * Scheduler job interface. * Will be called by the scheduler. * 該方法會執行觸發函式 */ Watcher.prototype.run = function run () { if (this.active) { var value = https://www.cnblogs.com/gxp69/p/this.get(); if ( value !== this.value || // Deep watchers and watchers on Object/Arrays should fire even // when the value is the same, because the value may // have mutated. isObject(value) || this.deep ) { // set new value var oldValue = https://www.cnblogs.com/gxp69/p/this.value; this.value =https://www.cnblogs.com/gxp69/p/ value; if (this.user) { try { this.cb.call(this.vm, value, oldValue); } catch (e) { handleError(e, this.vm, ("callback for watcher \"" + (this.expression) + "\"")); } } else { this.cb.call(this.vm, value, oldValue); } } } }; /** * Evaluate the getter, and re-collect dependencies. */ Watcher.prototype.get = function get () { pushTarget(this); var value; var vm = this.vm; try { value = this.getter.call(vm, vm); } catch (e) { if (this.user) { handleError(e, vm, ("getter for watcher \"" + (this.expression) + "\"")); } else { throw e } } finally { // "touch" every property so they are all tracked as // dependencies for deep watching if (this.deep) { traverse(value); } popTarget(); this.cleanupDeps(); } return value }; /** * Subscriber interface. * Will be called when a dependency changes. * 在方法中呼叫Watcher的run方法 */ Watcher.prototype.update = function update () { /* istanbul ignore else */ if (this.lazy) { this.dirty = true; } else if (this.sync) { this.run(); } else { queueWatcher(this);//該方法最終也會呼叫run方法 } }; /** * Depend on all deps collected by this watcher.會呼叫new Dep的depend方法，dep的depend會呼叫Watcher的addDep方法 */ Watcher.prototype.depend = function depend () { var i = this.deps.length; while (i--) { this.deps[i].depend(); } }; /** * Add a dependency to this directive. */ Watcher.prototype.addDep = function addDep (dep) { var id = dep.id; if (!this.newDepIds.has(id)) { this.newDepIds.add(id); this.newDeps.push(dep); if (!this.depIds.has(id)) { dep.addSub(this); } } };
轉載請註明出處，本文鏈接：https://www.uj5u.com/qiye/159519.html
標籤：JavaScript