Continuous tasks in nodejs - node.js

Question

i'am using nodejs with express for my webapp and i need to to run continuously
some code which checks if some data change and then update my mongodb.
How can i easily create a background process which runs the whole time together with the main task? So that the background task/process can inform the main task.
What i have tried already:
to solve this problem with a "setInterval" Function in the main process --> I works with no problem but think its not a good idea because it blocks the node event loop
Use child processes -> i could not found a good tutorial on them --> is there a easier method, perhaps a library which could help me?
some background worker libraries -->But do heavy-load tasks on the a child-process and finish but i need to do the work all the time
Update:
Final Solution:
UpdateEvent.js:
var events = require('events');
function Updater(time) {
this.time = time;
this.array = [
{number: 1},
{number: 2}
];
var that;
events.EventEmitter.call(this);
this.init = function()
{
that = this;
console.log("Contructor");
//Start interval
setInterval(that.run,that.time);
};
this.run = function()
{
that.array.forEach(function (item) {
if(item.number === 2)
{
that.emit('Event');
}
});
};
}
Updater.prototype.__proto__ = events.EventEmitter.prototype;
module.exports = Updater;
and then the code that uses it:
server.js:
var Updater = require('./UpdaterEvent');
var u = new Updater(10000);
u.init();
u.on('Event',function () {
console.log("Event catched!");
});
I followed the tutorial at:
http://www.sitepoint.com/nodejs-events-and-eventemitter/

Answer 1

The problem is the way you export your Updater constructor function:
exports.Updater = Updater;
When you require it, you do
var Updater = require('./UpdaterEvent');
and then try to run:
var u = new Updater(10000);
The problem is that you do not expose the function itself, but an object with a property called Updater which contains the function. Hence you either have to export it using
module.exports = Updater;
or you have to require it using:
var Updater = require('./UpdaterEvent').Updater;
Either way, then calling new Updater() will work. At the moment, you try to initialize a new object by calling an object instead of a constructor function, hence the error message:
TypeError: object is not a function

Answer 2

You should look into Events and EventEmitter
You could use child-process you don't really need to since JS is asynchronous. Just create a function for your background process and pass it your eventEmitter object. You can use setInterval or a while(true) loop to continuously check for the data change. When the data changes, call eventEmitter.emit('someEvent'); which will trigger a function in your main task to update your mongoDB.