TypeError: queue.Queue不是构造函数

Question

我正在学习用Node.js实现队列系统的redis。

使用文件"producer_worker.js“

// producer_worker.js
var redis = require("redis")
var client = redis.createClient();
var queue = require("./queue");
var logsQueue = new queue.Queue("logs", client);
var MAX = 5;
for (var i = 0;i < MAX; i++) {
    logsQueue.push("Hello world #" + i);
}
console.log("Created " + MAX + " logs");
client.quit();

和"queue.js“

function Queue(queueName, redisClient) {
    this.queueName = queueName;
    this.redisClient = redisClient;
    this.queueKey = "queues:" + queueName;
    this.timeout = 0;

    Queue.prototype.size = function (callback) {
        this.redisClient.llen(this.queueKey, callback);
    };
    Queue.prototype.push = function(data) {
        this.redisClient.lpush(this.queueKey, data);
    };
    Queue.prototype.pop = function(callback) {
        this.redisClient.brpop(this.queueKey, this.timeout, callback);
    };
    exports.Queue = Queue;  
}

当我尝试运行它时，它会产生错误：

node producer_worker.js 
var logsQueue = new queue.Queue("logs", client)
TypeError: queue.Queue is not a constructor

我已经检查了多次，以确保我的代码与book的代码一致。

我怎样才能修复TypeError？

Answer 1

这是因为您在执行Queue时将其导出。所以当你调用require('./queue')的时候，它显然还没有被导出。因此，为了解决这个问题，您需要在运行时导出Queue。

function Queue(queueName, redisClient) {
    this.queueName = queueName;
    this.redisClient = redisClient;
    this.queueKey = "queues:" + queueName;
    this.timeout = 0;
}

Queue.prototype.size = function (callback) {
    this.redisClient.llen(this.queueKey, callback);
};
Queue.prototype.push = function(data) {
    this.redisClient.lpush(this.queueKey, data);
};
Queue.prototype.pop = function(callback) {
    this.redisClient.brpop(this.queueKey, this.timeout, callback);
};
module.exports = Queue;  

// Usage
var Queue = require("./queue");
var logsQueue = new Queue("logs", client);

Answer 2

你必须从函数作用域中提取一些代码：

​

function Queue(queueName, redisClient) {
    this.queueName = queueName;
    this.redisClient = redisClient;
    this.queueKey = "queues:" + queueName;
    this.timeout = 0;
}

Queue.prototype.size = function (callback) {
    this.redisClient.llen(this.queueKey, callback);
};
Queue.prototype.push = function(data) {
    this.redisClient.lpush(this.queueKey, data);
};
Queue.prototype.pop = function(callback) {
    this.redisClient.brpop(this.queueKey, this.timeout, callback);
};
module.exports = { Queue: Queue };  

​