I am use express and express-ws in a node application. However, express-ws seems to be silencing errors making it very difficult to debug my code.
I've reduced my code down to just the following which still reproduces the problem:
// configure express
var express = require('express');
var app = express();
var expressWs = require('express-ws')(app);
// set up routes
app.get('/', function(req, res) {
console.log("GET");
nonExistingFunction(); // Called to demonstrate a traceback is provided.
});
app.ws('/', function(ws, req){
console.log("WS");
nonExistingFunction(); // Called to demonstrate this error is silenced.
});
// start service
app.listen(90);
When I GET from a browser, the console shows the 'GET' log message followed by the traceback (as expected). I.e;
GET
ReferenceError: nonExistingFunction is not defined
at C:\(project dir)\server.js:11:9
at Layer.handle [as handle_request] (C:\(project dir)\node_modules\express\lib\router\layer.js:95:5)
at next (C:\(project dir)\node_modules\express\lib\router\route.js:137:13)
at Route.dispatch (C:\(project dir)\node_modules\express\lib\router\route.js:112:3)
at Layer.handle [as handle_request] (C:\(project dir)\node_modules\express\lib\router\layer.js:95:5)
at C:\(project dir)\node_modules\express\lib\router\index.js:281:22
at Function.process_params (C:\(project dir)\node_modules\express\lib\router\index.js:335:12)
at next (C:\(project dir)\node_modules\express\lib\router\index.js:275:10)
at expressInit (C:\(project dir)\node_modules\express\lib\middleware\init.js:40:5)
at Layer.handle [as handle_request] (C:\(project dir)\node_modules\express\lib\router\layer.js:95:5)
When I connect via Websocket, the console just shows the 'WS' log message - no traceback. I.e;
WS
Does express-ws silence errors by default? Is there a way to switch it off?
I have a solution.
Express has its own default error handler which outputs the traceback to the console but allows the application to continue running. Express-ws uses a try-catch nest to do the same in wrap-middleware.js.
try {
/* Unpack the `.ws` property and call the actual handler. */
middleware(req.ws, req, next);
} catch (err) {
/* If an error is thrown, let's send that on to any error handling */
next(err);
}
However, this doesn't seem to get passed down to the default error handler. So instead, you can specify a error handler middleware for app. This must be the last middleware in the chain. The following code is a little hacky, but will output tracebacks to the console regardless of whether the error occurred within a HTTP or a WS route function.
// configure express
var express = require('express');
var app = express();
var expressWs = require('express-ws')(app);
// set up routes
app.get('/', function(req, res) {
console.log("GET");
nonExistingFunction(); // Called to demonstrate a traceback is provided.
});
app.ws('/', function(ws, req){
console.log("WS");
nonExistingFunction(); // Called to demonstrate this error is no longer silenced :)
});
// set up error handler
function errorHandler (err, req, res, next) {
if(req.ws){
console.error("ERROR from WS route - ", err);
} else {
console.error(err);
res.setHeader('Content-Type', 'text/plain');
res.status(500).send(err.stack);
}
}
app.use(errorHandler);
// start service
app.listen(90);