vue.js源码学习分享，九

/*  */

var arrayKeys = Object.getOwnPropertyNames(arrayMethods);//获取arrayMethods的属性名称

/**
 * By default, when a reactive property is set, the new value is//默认情况下，当一个响应的属性被设置，新的值也转换成响应的。然而当经过向下支撑时，我们不想促使转换，因为这值也许是一个嵌套值在一个冻结的数据结构，转换它时将会失去最优化
 * also converted to become reactive. However when passing down props,
 * we don't want to force conversion because the value may be a nested value
 * under a frozen data structure. Converting it would defeat the optimization.
 */
var observerState = {
  shouldConvert: true,
  isSettingProps: false
};

/**
 * Observer class that are attached to each observed//观察者类被绑定到每一个观察对象，一旦绑定，这个观察者使目标对象的属性键转换到getter/setter方法，收集依赖和发送的更新
 * object. Once attached, the observer converts target
 * object's property keys into getter/setters that
 * collect dependencies and dispatches updates.
 */
接下来是最关键的一部分

var Observer = function Observer (value) {
  this.value = value;
  this.dep = new Dep();
  this.vmCount = 0;
  def(value, '__ob__', this);//给value定义一个‘——ob——’属性，属性的值为这个Observer对象
  if (Array.isArray(value)) {//判断是不是一个数组
    var augment = hasProto
      ? protoAugment
      : copyAugment;
    augment(value, arrayMethods, arrayKeys);
    this.observeArray(value);
  } else {
    this.walk(value);
  }
};

/**
 * Walk through each property and convert them into//walk方法穿过每一个属性并且把他们转换到getter或者setter方法。这个方法应当仅在value的类型为对象时候调用
 * getter/setters. This method should only be called when
 * value type is Object.
 */
Observer.prototype.walk = function walk (obj) {
  var keys = Object.keys(obj);//获取对象的每个键
  for (var i = 0; i < keys.length; i++) {
    defineReactive$$1(obj, keys[i], obj[keys[i]]);
  }
};

/**
 * Observe a list of Array items.//观察一个数组项目的列表
 */
Observer.prototype.observeArray = function observeArray (items) {
  for (var i = 0, l = items.length; i < l; i++) {
    observe(items[i]);
  }
};

// helpers

/**
 * Augment an target Object or Array by intercepting//增加一个目标对象或者数组通过用__proto__截取原型链
 * the prototype chain using __proto__
 */
function protoAugment (target, src) {
  /* eslint-disable no-proto */
  target.__proto__ = src;
  /* eslint-enable no-proto */
}

/**
 * Augment an target Object or Array by defining
 * hidden properties.//增大一个目标对象或者数组通过定义隐藏的属性
 */
/* istanbul ignore next */
function copyAugment (target, src, keys) {
  for (var i = 0, l = keys.length; i < l; i++) {
    var key = keys[i];
    def(target, key, src[key]);
  }
}

/**
 * Attempt to create an observer instance for a value,//尝试创建一个观察者实例化一个值
 * returns the new observer if successfully observed,//返回一个新的观察者如果成功被观察
 * or the existing observer if the value already has one.//如果值已经有一个了则返回存在的观察者
 */
function observe (value, asRootData) {
  if (!isObject(value)) {//如果value不是对象，那么就到此结束
    return
  }
  var ob;
  if (hasOwn(value, '__ob__') && value.__ob__ instanceof Observer) {
    ob = value.__ob__;
  } else if (
    observerState.shouldConvert &&
    !isServerRendering() &&
    (Array.isArray(value) || isPlainObject(value)) &&
    Object.isExtensible(value) &&
    !value._isVue
  ) {
    ob = new Observer(value);
  }
  if (asRootData && ob) {
    ob.vmCount++;
  }
  return ob
}

/**
 * Define a reactive property on an Object.//定义一个响应的属性在一个对象上
 */
function defineReactive$$1 (
  obj,
  key,
  val,
  customSetter
) {
  var dep = new Dep();

  var property = Object.getOwnPropertyDescriptor(obj, key);
  if (property && property.configurable === false) {
    return
  }

  // cater for pre-defined getter/setters//满足预定义的  getter/setters
  var getter = property && property.get;
  var setter = property && property.set;

  var childOb = observe(val);
  Object.defineProperty(obj, key, {
    enumerable: true,
    configurable: true,
    get: function reactiveGetter () {
      var value = getter ? getter.call(obj) : val;
      if (Dep.target) {
        dep.depend();
        if (childOb) {
          childOb.dep.depend();
        }
        if (Array.isArray(value)) {
          dependArray(value);
        }
      }
      return value
    },
    set: function reactiveSetter (newVal) {
      var value = getter ? getter.call(obj) : val;
      /* eslint-disable no-self-compare */
      if (newVal === value || (newVal !== newVal && value !== value)) {
        return
      }
      /* eslint-enable no-self-compare */
      if ("development" !== 'production' && customSetter) {
        customSetter();
      }
      if (setter) {
        setter.call(obj, newVal);
      } else {
        val = newVal;
      }
      childOb = observe(newVal);
      dep.notify();
    }
  });
}

/**
 * Set a property on an object. Adds the new property and
 * triggers change notification if the property doesn't
 * already exist.
 */
function set (obj, key, val) {
  if (Array.isArray(obj)) {
    obj.length = Math.max(obj.length, key);
    obj.splice(key, 1, val);
    return val
  }
  if (hasOwn(obj, key)) {
    obj[key] = val;
    return
  }
  var ob = obj.__ob__;
  if (obj._isVue || (ob && ob.vmCount)) {
    "development" !== 'production' && warn(
      'Avoid adding reactive properties to a Vue instance or its root $data ' +
      'at runtime - declare it upfront in the data option.'
    );
    return
  }
  if (!ob) {
    obj[key] = val;
    return
  }
  defineReactive$$1(ob.value, key, val);
  ob.dep.notify();
  return val
}

/**
 * Delete a property and trigger change if necessary.
 */
function del (obj, key) {
  if (Array.isArray(obj)) {
    obj.splice(key, 1);
    return
  }
  var ob = obj.__ob__;
  if (obj._isVue || (ob && ob.vmCount)) {
    "development" !== 'production' && warn(
      'Avoid deleting properties on a Vue instance or its root $data ' +
      '- just set it to null.'
    );
    return
  }
  if (!hasOwn(obj, key)) {
    return
  }
  delete obj[key];
  if (!ob) {
    return
  }
  ob.dep.notify();
}

/**
 * Collect dependencies on array elements when the array is touched, since
 * we cannot intercept array element access like property getters.
 */
function dependArray (value) {
  for (var e = (void 0), i = 0, l = value.length; i < l; i++) {
    e = value[i];
    e && e.__ob__ && e.__ob__.dep.depend();
    if (Array.isArray(e)) {
      dependArray(e);
    }
  }
}