我正在尝试调用API，但出现错误

Question

我正在尝试调用Spotify API。当我运行Spotify.getSongs（）时，出现错误。这是我得到的错误：

TypeError：无法读取未定义的属性“ items”。

但是，当我将getSongs定义为该对象之外的函数时，它可以正常工作。如何拨打“ Spotify.getSongs（）”的电话？

let Spotify = {
  getOAuth() {
    fetch("https://accounts.spotify.com/api/token", {
      method: "POST",
      body:
        "grant_type=client_credentials&client_id=" +
        clientId +
        "&client_secret=" +
        clientSecret,
      headers: {
        "Content-Type": "application/x-www-form-urlencoded"
      }
    })
      .then(function(resp) {
        // Return the response as JSON
        return resp.json();
      })
      .then(function(data) {
        // Log the API data
        console.log("token", data);

        // Store token data
        this.token = data.access_token;
        this.tokenType = data.token_type;
        this.expires = new Date().getTime() + data.expires_in * 1000;
      })
      .catch(function(err) {
        // Log any errors
        console.log("something went wrong", err);
      });
  },

  getSongs() {
    return fetch(
      `https://api.spotify.com/v1/search?q=inception%20soundtrack&type=playlist`,
      {
        headers: {
          Authorization: this.tokenType + " " + this.token,
          "Content-Type": "application/json"
        }
      }
    )
      .then(resp => resp.json())
      .then(function(data) {
        console.log(data);
        let tracks = data.playlists.items[0].href;

        return fetch(
          `${tracks}/tracks?fields=items(track(name,artists(name),album(name,href)))`,
          {
            headers: {
              Authorization: this.tokenType + " " + this.token,
              "Content-Type": "application/json"
            }
          }
        );
      })
      .then(response => response.json())
      .then(data => {
        console.log(data);
        return data.items.map(info => ({
          name: info.track.name,
          artist: info.track.artists[0].name,
          album: info.track.album.name
        }));
      });
  }

  // If current token is invalid, get a new one
  // makeCall() {
  //   if (!this.expires || this.expires - new Date().getTime() < 1) {
  //     console.log("new call");
  //     this.getOAuth().then(function() {
  //       this.getSongs();
  //     });
  //   }
  // }
};