node.js - Require Exports Variables Errors - node.js

Question

I have a node.js script that does some database queries for me and works fine. The script is starting to get a bit longer so I thought I might start to break it up and thought moving the database connection code out to another file made sense.
Below is the code that I have moved into another file and then included with a require statement.
The issue I'm having is with the 'exports' commands at the bottom of the script. It appears the function 'dbHandleDisconnectUsers()' exports fine however the variable 'dbConnectionUsers' doesn't.
The script errors refer to methods of the object'dbConnectionUsers' (I hope thats the correct terminalogy) missing and gives me the impression I'm not really passing a complete object. Note: I would include the exact errors but I'm not in front of the machine.
var mysql = require('/usr/lib/node_modules/mysql');
// Users Database Configuration
var dbConnectionUsers;
var dbConfigurationUsers = ({
host : 'xxxxx',
user : 'xxxxx',
password : 'xxxxx',
database : 'xxxxxx',
timezone : 'Asia/Singapore'
});
// Users Database Connection & Re-Connection
function dbHandleDisconnectUsers() {
dbConnectionUsers = mysql.createConnection(dbConfigurationUsers);
dbConnectionUsers.connect(function(err) {
if(err) {
console.log('Users Error Connecting to Database:', err);
}else{
dbConnectionUsers.query("SET SESSION TRANSACTION ISOLATION LEVEL SERIALIZABLE;");
dbConnectionUsers.query("SET SESSION sql_mode = 'ANSI';");
dbConnectionUsers.query("SET NAMES UTF8;");
dbConnectionUsers.query("SET time_zone='Asia/Singapore';");
}
});
dbConnectionUsers.on('error', function(err) {
console.log('Users Database Protocol Connection Lost: ', err);
if(err.code === 'PROTOCOL_CONNECTION_LOST') {
dbHandleDisconnectUsers();
} else {
throw err;
}
});
}
dbHandleDisconnectUsers();
exports.dbHandleDisconnectUsers() = dbHandleDisconnectUsers();
exports.dbConnectionUsers = dbConnectionUsers;
In the core script I have this require statement:
var database = require('database-connect.js');
And I refer the function/variable as
database.dbHandleDisconnectUsers()
database.dbConnectionUsers

Answer 1

Ignoring the syntax error that everybody else has pointed out in exports.dbHandleDisconnectUsers() = dbHandleDisconnectUsers(), I will point out that dbConnectionUsers is uninitialized.
JavaScript is a pass-by-copy-of-reference language, therefore these lines:
var dbConnectionUsers;
exports.dbConnectionUsers = dbConnectionUsers;
are essentially identical to
exports.dbConnectionUsers = undefined;
Even though you set dbConnectionUsers later, you are not affecting exports.dbConnectionUsers because it holds a copy of the original dbConnectionUsers reference.
It's similar, in primitive data types, to:
var x = 5;
var y = x;
x = 1;
console.log(x); // 1
console.log(y); // 5
For details on how require and module.exports work, I will refer you to a recent answer I posted on the same topic:
Behavior of require in node.js

Answer 2

It's odd that your function is working but your other variable isn't exporting. This shouldn't be the case.
When you export functions you generally don't want to be exporting them as evaluated functions (ie. aFunction() ). The only time you might is if you want export whatever that function returns, or if you want to export an instance of a constructor function as part of your module.
The other thing, which is really odd, and is mentioned in a comment above is that you are trying to assign a value to exports.dbHandleDisconnectUsers(), which should be an undefined and throw an error.
So,in other words: Your code should not look like exports.whatever() = whatever().
Instead you should export both functions and other properties like this:
exports.dbHandleDisconnectUsers = dbHandleDisconnectUsers; // no evaluation ()
exports.dbConnectionUsers = dbConnectionUsers;
I don't know if this is the only thing wrong here, but this is definitely one thing that might be causing an execution error or two :)
Also, taking into consideration what Brandon has pointed out as well, you are initially exporting something undefined. But in your script, you are overwriting the reference anyway.
What you should do instead is make a new object reference, which is persistent and has a property in it that you can update. ie:
var dbConnection = {users: null};
exports.dbConnection = dbConnection;
Then when you run your function:
function dbHandleDisconnectUsers() {
dbConnection.users = mysql.createConnection(dbConfigurationUsers);
dbConnection.users.connect(function(err) {
if(err) {
console.log('Users Error Connecting to Database:', err);
}else{
dbConnection.users.query("SET SESSION TRANSACTION ISOLATION LEVEL SERIALIZABLE;");
dbConnection.users.query("SET SESSION sql_mode = 'ANSI';");
dbConnection.users.query("SET NAMES UTF8;");
dbConnection.users.query("SET time_zone='Asia/Singapore';");
}
});
dbConnection.users.on('error', function(err) {
console.log('Users Database Protocol Connection Lost: ', err);
if(err.code === 'PROTOCOL_CONNECTION_LOST') {
dbHandleDisconnectUsers();
} else {
throw err;
}
});
}
This way, the object reference of dbConnection is never overwritten.
You will then refer to your users db connection in your module as:
database.dbConnection.users
Your function should still work as you were intending on using it before with:
database.dbHandleDisconnectUsers();