Is Node Stateful? Can Node maintain variables in memory

Question

Is Node stateful?

If I want to build an index to keep in memory, will it persist throughout different connections? I'm just wondering if this is possible. For example we have a server in java that maintains a hashmap in memory to speed up certain search queries. It modifies it as things come in. Would this be possible in Node?

Thanks.

http://stackoverflow.com/questions/13179109/singleton-pattern-in-nodejs-is-it-needed - seems like modules are cached? — Ian, Jul 11 '14 at 14:05
I'd like to point out that, while you *can* build a server like this, you *shouldn't*, unless you're *sure* you'll *never* need to scale it to more than one server. — Stuart P. Bentley, Jul 11 '14 at 14:47
Thanks for pointing it out. I guess it makes sense that if it was scaling to a cluster of servers, that the indexes be unified somewhere accessible by the other servers. — William Falcon, Jul 11 '14 at 17:50

score 8 · Answer 1 · answered Jul 11 '14 at 14:09

Absolutely. Here's a dead-simple example of what I think you're looking for (modified sample code from http://nodejs.org):

var http = require('http');
var foo = 0;
http.createServer(function (req, res) {
  foo += 1;
  res.writeHead(200, {'Content-Type': 'text/plain'});
  res.end('You are foo number ' + foo + '\n');
}).listen(1337, '127.0.0.1');
console.log('Server running at http://127.0.0.1:1337/');

Note that this sort of thing often isn't done except for the most transient sort of data. If you something a little more persistent, look at using something like redis

score 3 · Accepted Answer · answered Jul 11 '14 at 14:04

3

Yes, you can keep state in your process that persists in memory for the lifetime of the process. There are libraries available for hashmaps, LRU caches, and other commonly-used data structures.

answered Jul 11 '14 at 14:04

Peter Lyons

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fmsf · Answer 3 · 2014-07-11T14:18:16.530

You can have the equivalent to static variables in node. The first time a file is required node will run the code in that file. Which means that if you define variables on a scope level equal or higher than the module.exports, you will always have access to those variables from inner closures.

(function(){
  var aStaticVariable = 123;

  module.exports = function() {
    // an instantiable object

  }
})();

You also have global variables:

global.aGlobalVar = "foo";

Is Node Stateful? Can Node maintain variables in memory

3 Answers3