Question

尝试在我的LobbyQueue类中访问和比较对象属性的值。我已经成功地将数据从server.js添加到阵列，并记录下来。但是当我尝试使用LobbyQueue类中的方法访问并比较数组中对象的属性值时，我得到了undefined作为数组索引。

我尝试从Queue类内部遍历数组的内容。这是我得到未定义的

的地方

LobbyQueue.js：

class LobbyQueue {
  constructor() {
    this.players = [];
  }
  enqueue(player) {
    this.players.push(player);
  }
  dequeue() {
    if (this.isEmpty()) {
      return "Wait List is Empty";
    }
    return this.players.shift();
  }
  hasUser(username) {
    if (this.players.length == 0) {
      return false;
    } else {
      for (var i = 0; i < this.players.length; ++i) {
        if (typeof this.players[i][username] === "undefined") {
          console.log("this.players[" + i + "][username] is undefined...");
          if (this.players[i][username] === username) {
            console.log("username comparison  entered...");
          }
        }
      }
    }
  }
}
module.exports = LobbyQueue;

server.js：

const queue = new LobbyQueue();
var gameRooms = [];

io.on("connection", socket => {
  console.log("a user connected..." + "\n");

  socket.on("addPlayer", username => {
    if (queue.hasUser(username)) {
      console.log("user already in queue...");
    } else {
      console.log("New user joined: " + username);
      queue.enqueue({
        username: username,
        id: socket.id
      });
      socket.join("lobby");

      const players = queue.getAll();
      console.log("Players in queue: " + "\n" + JSON.stringify(players));

      io.sockets.in("lobby").emit("players", players);
    }
  });
...

我希望hasUser()可以防止创建重复的连接。但当用户名已存在于队列中时，它不返回true。就像用户在数组上循环时不存在一样。但是由于队列已登录到控制台，并且用户名和连接ID在那里，所以我不确定发生了什么。

Answer 1

您需要将条件更改为

typeof this.players[i]['username'] === "undefined"

因为您需要访问属性名称“用户名”

for (var i = 0; i < this.players.length; ++i) {
        if (typeof this.players[i]['username'] === "undefined") {
          console.log("this.players[" + i + "][username] is undefined...");
          if (this.players[i]['username'] === username) {
            console.log("username comparison  entered...");
          }
        }
      }

Answer 2

def verify(number):
    return str(number).startswith("4")

将数组内容记录到控制台后，为什么未定义javascript数组对象？

2 个答案: