CODEWITHSUNDEEP
javascriptnode.js
Rishav Sharan
Rishav Sharan

Reputation: 2932

JS - passing a connection(object) from one function to another

I am new to JS and I have a simple question. I am writing a node_redis code to connect to the db. I have created a db module in which there is an init function to start the connection. the module also has another function which queries the db. for the query, i will need the connection (dbConnection) object from the first function and then use it in the 2nd function. how do i do this? I can get it done by using global variables but most places tell me its a bad idea.

Sorry if the question is stupid, I am learning how to code. results in google tell me that it can be done by passing it as an object property. But i don't know if it is the proper way to do things in my context, or even how to do it.

var redis = require('redis'); 

module.exports = redisDb = {
// Initialize the module. Invokes callback when ready (or on error)
init: function(config, callback) {

    // Open the database connection
    var dbConnection = redis.createClient(config.db.port, config.db.host, {no_ready_check: true}); 

    dbConnection.auth(config.db.authKey, function() {
        console.log("Connected!");
        console.log(dbConnection.keys('*'));
    });

    dbConnection.on('connect'     , log('connect'));
    dbConnection.on('ready'       , log('ready'));
    dbConnection.on('reconnecting', log('reconnecting'));
    dbConnection.on('error'       , log('error'));
    dbConnection.on('idle'         , log('idle...'));
    dbConnection.on('end'         , log('end'));

    function log(type) {
        return function() {
            console.log(type, arguments);
        }
    }
    callback("callback - Connected");
},

getValue: function(key, callback) {
    dbConnection.hgetall("hosts", function (err, obj) {
    console.dir(obj);
    });
}
};

EDIT: tried another way. still failing.

module.exports = redisDb = (function() {
var config = require('../config');
var redis = require('redis'); 

return {
    connection: function(config) {
        var dbConnection = redis.createClient(config.db.port, config.db.host, {no_ready_check: true}); 

        dbConnection.auth(config.db.authKey, function() {
            console.log("Authenticated!");
        });
        return dbConnection
    },
    getValue: function(connection, callback) {
        connection.hgetall("hosts", function (err, obj) {
        console.dir(obj);
        });
    }
}
})();

Upvotes: 1

Views: 1563

Answers (2)

Rishav Sharan
Rishav Sharan

Reputation: 2932

I made the code work by simply declaring the connection in the parent function.

module.exports = _redisDb = (function() {

    var redis = require('redis'); 
    var config = require('../config');

    var dbConnection = redis.createClient(config.db.port, config.db.host, {no_ready_check: true});
    dbConnection.auth(config.db.authKey, function() {
        console.log("Authenticated!");
    });

    var getValue = function() {
            dbConnection.hgetall("hosts", function (err, obj) {
            console.dir(obj);
            });
        }

    return {
        getValue: getValue
    }
})();

While the above work,s I'd still like for someone to tell me how can I pass variables/objects between functions off the same module.

Upvotes: 0

Kokozaurus
Kokozaurus

Reputation: 639

Now one way is as you said to make dbConnection an object Property. The other way is to call init() in getValue() which results in establishing different connection every time you want some value.

Because a DB Connection is a valuable resource, I'd say it's better to use the second variant. Of course then you'll need to return dbConnection from init().

PS: Global variables were made initially for such things and then people saw that fewer they are the better. That's why using global vars is considered a bad style.

Upvotes: 1

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