how to handle unhandled exceptions in libraries in node.js

Question

I have a node.js application using Express and Redis. My question is how do I catch and handle a Redis connection error. I have an app.error function in express which handles most application errors but since this error is an error that gets thrown in the redis library it becomes an uncaught exception and the whole app goes down.

Can I just define an on_error method on my redis client and that will do the trick? If so maybe some sample code? Should I somehow handle it in a node.js next tick error? I'm not sure I understand the next statement exactly so not sure what's the best practice.

In the code below the catch block never gets hit even if there is a connection error

try
{ 
  feedClient = redis.createClient(feedPort, feedHost);
}
catch (error)
{
  console.log('cannnot start redis' + error);
}

Here's the uncaught error

node.js:134
        throw e; // process.nextTick error, or 'error' event on first tick
        ^
Error: Redis connection to localhost:6379 failed - ECONNREFUSED, Connection refused
    at RedisClient.on_error (/node_modules/redis/index.js:136:24)
    at Socket. (/node_modules/redis/index.js:70:14)
    at Socket.emit (events.js:64:17)
    at Array. (net.js:830:27)
    at EventEmitter._tickCallback (node.js:126:26)

Almost duplicate to stackoverflow.com/q/8071291/638546

Akseli Palén
– Akseli Palén

2013-03-12 09:46:37 +00:00
Commented Mar 12, 2013 at 9:46 — Akseli Palén
– Akseli Palén, Commented Mar 12, 2013 at 9:46

Linus Thiel · Accepted Answer · 2012-02-16 17:22:01Z

10

Yes, you need to specify an error handler:

feedClient = redis.createClient(feedPort, feedHost);
feedClient.on("error", function(err) {
  console.error("Error connecting to redis", err);
});

answered Feb 16, 2012 at 17:22

Linus Thiel

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2 Comments

King Friday Over a year ago

yah i was only handling it for one redis connection, had 3, didn't handle other two, couldn't figure out why was crapping out. +1

Achim Koellner Over a year ago

The redis node-module is internally prototyping EventEmitter.

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