无法为打字稿字典赋值

Question

我创建了一个打字稿词典。当我为其赋值时，出现以下错误。

         TypeError: Cannot set property 'v1/items/someItemType/someItemId/EVENT/some
    DataTypeId' of undefined
          at MainClass.subscribe (G:\Projects\src\main\MainClass
    .js:9:3522)
          at Context.<anonymous> (G:\Projects\test\main\Wish.
    spec.js:45:18)
          at callFn (G:\Projects\node_modules\mocha\lib\runna
    ble.js:315:21)
          at Hook.Runnable.run (G:\Projects\node_modules\moch
    a\lib\runnable.js:308:7)
          at next (G:\Projects\node_modules\mocha\lib\runner.
    js:298:10)
          at Immediate._onImmediate (G:\Projects\node_modules
    \mocha\lib\runner.js:320:5)

下面是我声明字典的方式。

interface StringTopicToMyTopicMap {
  [topic: string]: MyTopic;
};

下面是MyTopic的界面。

export interface MyTopic {
  dataTypeID: string;
  itemID: string;
  itemType: string;
  dataType: MyDataType;
  qos: number;
}

然后我试着给这个字典赋值，如下所示。

private subscriptionTopicsMap: StringTopicToMyTopicMap;

subscribe(myTopic: MyTopic) {
    if (_.isEmpty(myTopic)) {
      throw new MyError('myTopic cannot be empty');
    } else {
      let topic: string;
      topic = 'v1/items/' + myTopic.itemType + '/' + myTopic.itemID + '/'
        + myTopic.dataType + '/' + myTopic.dataTypeID;
      this.subscriptionTopicsMap[topic] = myTopic;
      this.client.subscribe(topic);
    }
  }

行中抛出错误，

this.subscriptionTopicsMap[topic] = myTopic;

我是打字稿的新手。我在这里做错了什么？请指教

Answer 1

你还没有初始化你的 subscriptionTopicsMap 词典，此外，您没有任何 class 实现 StringTopicToMyTopicMap，并且可以实例化

  class StringTopicToMyTopicMapClass implements StringTopicToMyTopicMap {
         [topic: string]: MyTopic;
  };

  private subscriptionTopicsMap: StringTopicToMyTopicMap = new StringTopicToMyTopicMapClass ();

Answer 2

只需在声明时初始化您的属性

//private subscriptionTopicsMap: StringTopicToMyTopicMap;
private subscriptionTopicsMap: StringTopicToMyTopicMap = {};

Answer 3

我通常这样做比较简单，不需要第二个界面。同样如前所述，您将需要 ={} 如下：

private subscriptionTopicsMap: { [id: string]: MyTopic; } = {};
this.subscriptionTopicsMap[topic] = myTopic;

无法为打字稿字典赋值

Unable to assign value to typescript dictionary

javascript

dictionary

typescript

typescript1.8