CODEWITHSUNDEEP
javascriptnode.js
Wizard
Wizard

Reputation: 22113

TypeError: queue.Queue is not a constructor

I am learning redis with Node.js to implement the Queue system

with file "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();

and "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;  
}

It generates error when I tried to run it :

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

I have checked multiple times to ensure my codes consistent with those of book.

How could I fix the TypeError?

Upvotes: 0

Views: 3152

Answers (2)

Bartłomiej Gładys
Bartłomiej Gładys

Reputation: 4615

You have to pull off some of your code from function scope:

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 };

Upvotes: 1

Lewis
Lewis

Reputation: 14906

It's because you're exporting Queue when executing it. So it obviously hasn't yet been exported when you call require('./queue'). So in order to fix this, you need to export Queue on runtime instead.

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);

Upvotes: 2

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