CODEWITHSUNDEEP
node.jsexceptioneventshandle
Andrey Reeshkov
Andrey Reeshkov

Reputation: 361

nodejs handle exception in events handler: safeway?

There is another true way, to do safe handle exceptions in nodejs events unsafe handlers? I can't control event handlers, but application must run after errors in it.

var someUnsafeEventHandler = function(){ throw "throw!"; };

var MySafeEventHandler = function(f){
    return function(){
        try{ 
            f.apply(f,arguments);
        }catch(e){
            console.warn("MySafeEventHandler handle error: "+e);
        };
    }
}

var EventEmitter = require('events');
var myEmitter = new EventEmitter();

myEmitter.on('event', new MySafeEventHandler(someUnsafeEventHandler));
myEmitter.on('event', someUnsafeEventHandler);

console.log("== start test ==");
myEmitter.emit('event');
console.log("== test passed =="); // never printed by exception in someUnsafeEventHandler

output:

== start test ==
MySafeEventHandler handle error: throw!

/tmp/test_events.js:5
var someUnsafeEventHandler = function(){ throw "throw!"; };
                                         ^
throw!

Upvotes: 1

Views: 354

Answers (1)

Dmitriy Mozgovoy
Dmitriy Mozgovoy

Reputation: 1597

It's a bad practice to swallow errors, so it's better to redirect errors to a special error event defined in EventEmitter.

var someUnsafeEventHandler = function(){ throw "throw!"; };

const safeHandler= (f)=> function(){
    try{
        f.apply(this, arguments);
    }catch(e){
        this.emit('error', e);
    }
}

var EventEmitter = require('events');
var myEmitter = new EventEmitter();

// catch errors
myEmitter.on('error', e=> console.log(`Caught: ${e}`));

myEmitter.on('event', safeHandler(someUnsafeEventHandler));
myEmitter.on('event', ()=> console.log('second listener'));

console.log("== start test ==");
myEmitter.emit('event');
console.log("== test passed ==");

Output:

== start test ==
Caught: throw!
second listener
== test passed ==

Process finished with exit code 0

Upvotes: 2

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