CODEWITHSUNDEEP
javascriptnode.js
Catfish
Catfish

Reputation: 19294

File with variable that gets updated, and other files see that change?

I'm trying to build a simple tool that pings a bunch of url's to monitor their status and it updates a variable with each app's status.

I also have another file which i'd like to be able to execute at any time to get the current status of each app from that variable.

Here's my main file and you can see there are 2 exports - start, and getStatuses.

index.js

'use strict';

const rest = require('restler');
const time = require('simple-time');
const seconds = time.SECOND;

// The list of apps to check if are running
var apps = {
  myApp: {
    url: 'http://myUrl.com',
    status: null,
    lastUpdatedAt: new Date()
  }
};

/**
 * Loop through and check the status of every app
 */
function checkAllStatuses() {
  for (var name in apps) {
    if (apps.hasOwnProperty(name)) {

      var app = apps[name];
      console.log('app = ', app);
      checkAppStatus(name, app);
    }
  }
}

/**
 * Checks the status of an app
 *
 * @param name  - The name of the app
 * @param app   - The app that we're checking the status of
 */
function checkAppStatus(name, app) {

  var req = rest.get(app.url);

  req.on('complete', function(result, response) {
    if(response.statusCode !== app.status) {
      updateStatus(name, response.statusCode);
    }
  });

  req.on('error', function(e) {
    console.log('ERROR: ' + e.message);
  });

  req.on('timeout', function(data, response) {
    console.log('Request timed out');
  });

}

/**
 * Updates the status of an app
 * 
 * @param app     - The app to update the status of
 * @param status  - The status to update the app to
 */
function updateStatus(name, status) {
  apps[name].status = status;
  apps[name].lastUpdatedAt = new Date();
}

function getStatuses() {
  return apps;
}

function start() {
  // Check every 5 seconds
  setInterval(checkAllStatuses, 5*seconds);
}

module.exports.start = start;
module.exports.getStatuses = getStatuses;

Then i have a file which starts the process:

start.js

'use strict';

const status = require('./index');

status.start();

Then i have a file that I want to execute to get the current status of the apps:

consume.js

'use strict';

const status = require('./index');

console.log(status.getStatuses());

The problem is that consume.js just displays exactly what's in the initial app variable in index.js which is:

{
      myApp: {
        url: 'http://myUrl.com',
        status: null,
        lastUpdatedAt: new Date()
      }
    };

while the process running the start() command is displaying an updated status that is NOT null.

How can I make it so consume.js can see the value of a variable that start.js is updating?

I'd like to not have to use a datastore if possible. Worst case scenario is i write to a file, run redis, mongo, or some other datastore but i'm trying to avoid that making this app as simple as possible.

Upvotes: 0

Views: 41

Answers (1)

Justin Heath
Justin Heath

Reputation: 401

You are using the same code, index.js in both start.js and consume.js, but creating two separate instances of it when you run each file. That is, the apps variable is changing in the instance created by start.js, but nothing in consume.js tells your code to change the apps variable.

If you are not saving a history of statuses, or saving the data to a datastore, what's the point in the start routine? You could just call checkAllStatuses and then return the results when you wish to consume the data.

Edit Here's an example of combining the two files (start.js and consume.js) into one file. It also adds in a sample socket.io implementation since you stated that providing the statuses via websockets to clients was the evntual goal.

var app = require('http').createServer(handler)
var io = require('socket.io')(app);
var fs = require('fs');
//// Your status library
var status = require('./index');

//// Start getting statuses
status.start();
app.listen(80);

//
// This is just the default handler
//   in the socket.io example
//
function handler (req, res) {
  fs.readFile(__dirname + '/index.html',
  function (err, data) {
    if (err) {
      res.writeHead(500);
      return res.end('Error loading index.html');
    }

    res.writeHead(200);
    res.end(data);
  });
}

io.on('connection', function (socket) {

  // Someone wants the list of statuses
  //   This uses socket.io acknowledgements
  //   to return the data. You may prefer to use 
  //   `socket.emit` instead or an altogether different socket library.
  socket.on('status_fetch', function (data, callback_fn) {
    callback_fn( status.getStatuses() );
  });

});

Upvotes: 1

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