Node.js Exception handling Unhanded Exception Management
Example
Because Node.js runs on a single process uncaught exceptions are an issue to be aware of when developing applications.
Silently Handling Exceptions
Most of the people let node.js server(s) silently swallow up the errors.
- Silently handling the exception
process.on('uncaughtException', function (err) {
console.log(err);
});
This is bad, it will work but:
-
Root cause will remains unknown, as such will not contribute to resolution of what caused the Exception ( Error ).
-
In case of database connection ( pool ) gets closed for some reason this will result in constant propagation of errors, meaning that server will be running but it will not reconnect to db.
Returning to Initial state
In case of an " uncaughtException " it is good to restart the server and return it to its initial state, where we know it will work. Exception is logged, application is terminated but since it will be running in a container that will make sure that the server is running we will achieve restarting of the server ( returning to the initial working state ) .
- Installing the forever ( or other CLI tool to make sure that node server runs continuously )
npm install forever -g
- Starting the server in forever
forever start app.js
Reason why is it started and why we use forever is after the server is terminated forever process will start the server again.
- Restarting the server
process.on('uncaughtException', function (err) {
console.log(err);
// some logging mechanisam
// ....
process.exit(1); // terminates process
});
On a side note there was a way also to handle exceptions with Clusters and Domains.
Domains are deprecated more information here.
