javascript - 访问类中的构造函数属性

Question

当涉及到对象变量时，我不理解 JavaScript 作用域。我定义了以下类:

class DataHandler {
  constructor(boardIDA, boardIDB, accessToken, eventA, eventB) {
    this.times = [];
    this.eventA = eventA;
    this.eventB = eventB;
    this.apiURLA = "https://api.particle.io/v1/devices/" + boardIDA + "/events/" + eventA + "/?access_token=" +
      accessToken;
    this.apiURLB = "https://api.particle.io/v1/devices/" + boardIDB + "/events/" + eventB + "/?access_token=" + accessToken;
    this.eventListenerA = new EventSource(this.apiURLA);
    this.eventListenerB = new EventSource(this.apiURLB);
    this.addListener(this.eventListenerA,
      eventA);
    this.addListener(this.eventListenerB, eventB);
  }
  addListener(eventSrc, eventName) {
    eventSrc.addEventListener(eventName, function(info) {
      alert(eventName);
      var parsedData = JSON.parse(info.data);
      this.times.push(parsedData);
    });
  }
}

问题出在 this.times 。我已经在构造函数中声明了它。但是，我似乎无法在 addListener 中访问它— 我收到一条错误消息，说我正在尝试调用 push上undefined 。我做错了什么？

Answer 1

您没有在 addListener 中访问它，而是尝试在匿名事件处理程序中访问它，该处理程序使用不同的 this 进行调用。

addListener(eventSrc, eventName) {
  var handler = function(info) {
    alert(eventName);
    var parsedData = JSON.parse(info.data);
    this.times.push(parsedData);
  };
  eventSrc.addEventListener(eventName, handler.bind(this));
}