嵌套的ES6代理无法按预期工作

时间:2016-06-03 08:52:48

标签: javascript node.js ecmascript-6 es6-proxy

我正在开发一个API客户端,允许在提供foo的ID时调用特定的API方法,如下所示:

apiClient.myApiMethod('myFooId', 'firstApiArg', 'nthApiArg');

为方便开发人员,我尝试实现自定义代理对象:

var myFoo = apiClient.registerFoo('myFoo', 'myFooId');
myFoo.myApiMethod('firstApiArg', 'nthApiArg');

在搜索了一段时间之后,我认为ES6代理可能最适合它,因为fooId需要作为方法调用的第一个参数插入以支持两种工作方式。
因此,我创建了以下代码。如果调用Foo.myFoos的对象属性(例如Foo.myFoos.example),则在_myFooItems中搜索它,如果它存在,则返回另一个Proxy对象。
现在,如果在 对象上调用方法,则会在Foo的属性中搜索该方法,如果找到,则使用Foo调用myFooId方法作为第一个论点 这意味着,您应该能够Foo.myFoos.example.parentMethodX('bar', 'baz')

var Foo = function() {

  // parent instance
  _self = this;

  // custom elements dictionary
  _myFooItems = {};

  // to call parent methods directly on custom elements
  this.myFoos = Object.create(new Proxy({}, {

      // property getter function (proxy target and called property name as params)
      get: function(target, myFooName) {

        // whether called property is a registered foo
        if (_myFooItems.hasOwnProperty(myFooName)) {

          // create another proxy to intercept method calls on previous one
          return Object.create(new Proxy({}, {

              // property getter function (proxy target and called property name as params)
              get: function(target, methodName) {

                // whether parent method exists
                if (_self.hasOwnProperty(methodName)) {

                  return function(/* arguments */) {

                    // insert custom element ID into args array
                    var args = Array.prototype.slice.call(arguments);
                    args.unshift(_myFooItems[ myFooName ]);

                    // apply parent method with modified args array
                    return _self[ methodName ].apply(_self, args);
                  };
                } else {

                  // parent method does not exist
                  return function() {
                    throw new Error('The method ' + methodName + ' is not implemented.');
                  }
                }
              }
            }
          ));
        }
      }
    }
  ));


  // register a custom foo and its ID
  this.registerFoo = function(myFooName, id) {

    // whether the foo has already been registered
    if (_myFooItems.hasOwnProperty(myFooName)) {
      throw new Error('The Foo ' + myFooName + ' is already registered in this instance.');
    }

    // register the foo
    _myFooItems[ myFooName ] = id;

    // return the created foo for further use
    return this.myFoos[ myFooName ];
  };
};

module.exports = Foo;

虽然如果运行代码并尝试注册foo会发生什么(上面的代码在Node> = 6.2.0中工作),是否会引发以下错误:

> var exampleFoo = Foo.registerFoo('exampleFoo', 123456)
Error: The method inspect is not implemented.
  at null.<anonymous> (/path/to/module/nestedProxyTest.js:40:31)
  at formatValue (util.js:297:21)
  at Object.inspect (util.js:147:10)
  at REPLServer.self.writer (repl.js:366:19)
  at finish (repl.js:487:38)
  at REPLServer.defaultEval (repl.js:293:5)
  at bound (domain.js:280:14)
  at REPLServer.runBound [as eval] (domain.js:293:12)
  at REPLServer.<anonymous> (repl.js:441:10)
  at emitOne (events.js:101:20)

在花了很多时间考虑为什么第二个代理甚至试图调用一个方法,如果没有给它,我最终放弃了。我希望exampleFoo成为一个代理对象,如果被调用则接受Foo方法 是什么导致了这里的实际行为?

2 个答案:

答案 0 :(得分:3)

我认为你根本不应该使用代理。假设您的API具有可怕的

  openUploadDialog() {
    if (this.dialog) {
      this.dialog.instance.openModal();
      return;
    }

    this._resolver.resolveComponent(MyDialog).
      then(factory => {
        const injector = ReflectiveInjector.fromResolvedProviders([],
          this._container.injector);
        this.dialog = this._container.createComponent(
          factory, null, injector, []);
      });
  }

那么实现你所期待的最简洁的方法是

class Foo {
    …
    myApiMethod(id, …) { … }
    … // and so on
}

这样你就可以了

const cache = new WeakMap();
Foo.prototype.register = function(id) {
    if (!cache.has(this))
        cache.set(this, new Map());
    const thisCache = cache.get(this);
    if (!thisCache.get(id))
        thisCache.set(id, new IdentifiedFoo(this, id));
    return thisCache.get(id);
};

class IdentifiedFoo {
    constructor(foo, id) {
        this.foo = foo;
        this.id = id;
    }
}
Object.getOwnPropertyNames(Foo.prototype).forEach(function(m) {
    if (typeof Foo.prototype[m] != "function" || m == "register") // etc
        return;
    IdentifiedFoo.prototype[m] = function(...args) {
        return this.foo[m](this.id, ...args);
    };
});

答案 1 :(得分:1)

首先,我不确定代理模式是处理问题的最有效和最干净的方式,但它当然应该可行。

我看到的第一个问题是你的实际测试试图在Foo原型(类)本身上调用registerFoo,而你只为Foo的实例定义了它。所以你必须先创建一个实例,如下所示:

var foo = new Foo();
var exampleFoo = foo.registerFoo('exampleFoo', 123456);

然后要完成测试,你必须调用一个应该存在的方法。所以为了测试它,我会添加Foo这样的东西:

  // Define an example method on a Foo instance:
  this.myMethod = function (barName /* [, arguments] */) {
    var args = Array.prototype.slice.call(arguments);
    return 'You called myMethod(' + args + ') on a Foo object';
  }

虽然不是问题,但我认为没有必要在Object.create上应用new Proxy(...),因为后者已经创建了一个对象,我认为使用它作为原型没有好处直接使用它作为你的对象。

所以通过这些微小的调整,我得到了这个代码,它似乎在浏览器中产生了正确的结果(在这里使用FireFox):

var Foo = function() {
  // parent instance
  _self = this;
  // example method
  this.myMethod = function (barName /* [, arguments] */) {
    var args = Array.prototype.slice.call(arguments);
    return 'You called myMethod(' + args + ') on a Foo object';
  }
  // custom elements dictionary
  _myFooItems = {};
  // to call parent methods directly on custom elements
  this.myFoos = new Proxy({}, {
      // property getter function (proxy target and called property name as params)
      get: function(target, myFooName) {
        // whether called property is a registered foo
        if (_myFooItems.hasOwnProperty(myFooName)) {
          // create another proxy to intercept method calls on previous one
          return new Proxy({}, {
              // property getter function (proxy target and called property name as params)
              get: function(target, methodName) {
                // whether parent method exists
                if (_self.hasOwnProperty(methodName)) {
                  return function(/* arguments */) {
                    // insert custom element ID into args array
                    var args = Array.prototype.slice.call(arguments);
                    args.unshift(_myFooItems[ myFooName ]);
                    // apply parent method with modified args array
                    return _self[ methodName ].apply(_self, args);
                  };
                } else {
                  // parent method does not exist
                  return function() {
                    throw new Error('The method ' + methodName + ' is not implemented.');
                  }
                }
              }
          });
        }
      }
  });

  // register a custom foo and its ID
  this.registerFoo = function(myFooName, id) {
    // whether the foo has already been registered
    if (_myFooItems.hasOwnProperty(myFooName)) {
      throw new Error('The Foo ' + myFooName + ' is already registered in this instance.');
    }
    // register the foo
    _myFooItems[ myFooName ] = id;
    // return the created foo for further use
    return this.myFoos[ myFooName ];
  };
};

// Test it:
var foo = new Foo();
var exampleFoo = foo.registerFoo('exampleFoo', 123456);
var result = exampleFoo.myMethod(13);
console.log(result);