javascript - notifier.performChange实际做什么？

我试图了解Object.getNotifier(object).performChange。从概念上讲，我知道它是为定义“宏观”或更高级更改而设计的。从example everyone seems to refer to:

increment: function(amount) {
  var notifier = Object.getNotifier(this);

  notifier.performChange(Thingy.INCREMENT, function() {
    this.a += amount;
    this.b += amount;
  }, this);

  notifier.notify({
    object: this,
    type: Thingy.INCREMENT,
    incremented: amount
  });
}

我不明白的是，这与直接执行传递给notifier.performChange而不是作为回调的匿名函数有何不同？换句话说，它与以下内容有何不同:

increment: function(amount) {
  var notifier = Object.getNotifier(this);

  this.a += amount;
  this.b += amount;

  notifier.notify({
    object: this,
    type: Thingy.INCREMENT,
    incremented: amount
  });
}

我已经看到，在最新的规范中，notifier.performChange可能返回一个对象，然后将该对象作为通知发出，如:

notifier.performChange(Thing.INCREMENT, function() {
    this.a += amount;
    this.b += amount;

    // a notification is issues with this return value,
    // including the type passed to notifier.performChange,
    // and the object underlying notifier.
    return {incremented: amount};
});

这就消除了在原始代码中使用以下notifier.notify的需要，但是，这仍然不是糖，还是在功能上与仅进行更改并自己发出通知之间存在功能差异？

最佳答案

经过一个小时的大量测试，我终于弄明白了。我有相同的问题(performChange代表什么？)，也有相同的想法将其删除并致电

this.a += amount;
this.b += amount;

但是:notifier.performChange的要点是，观察者不会观察到每个更改。

我正在像这样测试它:

var obj = {
  x: 5,
  y: 10
};

function noti() {
  console.log('noti start');
  var notifier = Object.getNotifier(obj);

  notifier.performChange('ok', function() {
    obj.x++;
    obj.y++;
  });

  notifier.notify({
    type: 'ok',
    oldValue: 5
  });
  console.log('noti end');
};

function noti2() {
  console.log('noti2 start');
  var notifier = Object.getNotifier(obj);

  obj.x++;
  obj.y++;

  notifier.notify({
    type: 'ok',
    oldValue: 5
  });
  console.log('noti2 end');
};

function observer(changes) {
  for (var change of changes) {
    console.log('observer: change =', change, ' newValue=', change.object[change.name]);
  }
};

Object.observe(obj, observer, ['ok', 'update']);

console.log('calling noti2()');
noti2(); //will log the changes of update twice becuase of the x and y property of obj

// add delay manually because observer calls are asynchronous and
// we want to clearly separate the notification function calls in our logs
setTimeout(function() {
  console.log('calling noti()');

  noti(); //will only log the ok type. that's what they mean by big change
          //so everything you do inside the performChange won't be observed
}, 100);

它应该返回以下控制台输出:

calling noti2()
noti2 start
noti2 end
observer: change = Object {type: "update", object: Object, name: "x", oldValue: 5}  newValue= 6
observer: change = Object {type: "update", object: Object, name: "y", oldValue: 10}  newValue= 11
observer: change = Object {object: Object, type: "ok", oldValue: 5}  newValue= undefined

calling noti()
noti start
noti end
observer: change = Object {object: Object, type: "ok", oldValue: 5}  newValue= undefined