JavaScript代理的替代方案

Ovilia 发表于 Dev

奥维利亚

我想Proxy在ObservableList包含一个的自定义类上使用Array。由于Proxy仅在ES6之后才可用，所以我想知道是否还有其他替代实现。

我的要求是，一旦ObservableList更改，就可以更新（而不是引起注意）观察者，以便观察者始终可以通过某种过滤或映射方法观察到。

var activities = new ObservableList(['reading', 'swimming']);
var sAct = activities.filter(function(v) {
  return v[0] === 's';
});
// expect sAct.list to be ['swimming']
var meAct = activities.map(function(v) {
  return 'I am ' + v;
});
// expect meAct.list to be ['I am reading', 'I am swimming']

activities.list.push('smiling');
console.log(sAct.list, meAct.list);
// expect sAct.list to be ['swimming', 'smiling']
// expect meAct.list to be ['I am reading', 'I am swimming', 'I am smiling']

activities.list[1] = 'snoopying';
console.log(sAct.list, meAct.list);
// expect sAct.list to be ['swimming', 'snoopying']
// expect meAct.list to be ['I am reading', 'I am snoopying', 'I am smiling']

我对Proxy的实现可在https://jsfiddle.net/ovilia/tLmbptr0/3/

奥维利亚

如题所述，我只需要ObservableList到包含的Array，而不是扩大它，因为吉姆在他做了复杂的答案。而且令人惊讶的是，我发现可以通过包装原始Array操作轻松地实现这一点。

一个限制是索引操作在我的实现中不是被动的，因为我没有找到捕获索引操作的正确方法。如果您有更好的主意，欢迎告诉我！XD

这是完整的实现。

export class ObservableList {

  list: Array<any>;

  private _observer: Array<ObserverList>;

  constructor(list?: Array<any>) {
    this.list = list || [];
    this._initList();
    this._initMethods();

    this._observer = [];
  }

  notify(): void {
    for (let o of this._observer) {
      o.update();
    }
  }

  private _initList(): void {
    var that = this;
    var operations = ['push', 'pop', 'shift', 'unshift', 'splice',
      'sort', 'reverse'];
    for (let operation of operations) {
      this.list[operation] = function() {
        var res = Array.prototype[operation].apply(that.list, arguments);
        that.notify();
        return res;
      }
    }
  }

  private _initMethods(): void {
    var that = this;
    var methods = ['filter', 'map'];
    for (let method of methods) {
      this[method] = (formatter: Function): ObserverList => {
        var observer = new ObserverList(that, formatter, method);
        this._observer.push(observer);
        return observer;
      }
    }
  }

}

export class ObserverList {

  public list: Array<any>;

  constructor(public observable: ObservableList, 
              public formatter: Function, 
              public method: string) {
    this.list = [];
    this.update();
  }

  update(): void {
    var list = [];
    var master = this.observable.list;
    for (var i = 0, len = master.length; i < len; ++i) {
      if (this.method === 'filter') {
        if (this.formatter(master[i])) {
          list.push(master[i]);
        }
      } else if (this.method === 'map') {
        list.push(this.formatter(master[i]));
      } else {
        console.error('Illegal method ' + this.method + '.');
      }
    }
    this.list = list;
  }

}