Javascript Asynchronous Exception Handling with node.js

Question

I\'m currently working on a node.js app and I\'m having the usual asynchronous code issue.

I\'m implementing a service server on top of Node\'s HTTP module.

Answer 1

Warning: I would not recommend the original answer using domains, domains are being deprecated in the future, I had a lot of fun writing the original answer but I no longer believe it is too relevant. Instead - I suggest using event emitters and promises that have better error handling - here is the below example with promises instead. The promises used here are Bluebird:

Promise.try(function(){ 
    throw new Error("Something");
}).catch(function(err){
    console.log(err.message); // logs "Something"
});

With a timeout (note that we have to return the Promise.delay):

Promise.try(function() {
    return Promise.delay(1000).then(function(){
        throw new Error("something");
    });
}).catch(function(err){
    console.log("caught "+err.message);
});

With a general NodeJS funciton:

var fs = Promise.promisifyAll("fs"); // creates readFileAsync that returns promise
fs.readFileAsync("myfile.txt").then(function(content){
    console.log(content.toString()); // logs the file's contents
    // can throw here and it'll catch it
}).catch(function(err){
    console.log(err); // log any error from the `then` or the readFile operation
});

This approach is both fast and catch safe, I recommend it above the below answer which uses domains that are likely not here to stay.

---

I ended up using domains, I have created the following file I called mistake.js which contains the following code:

var domain=require("domain");
module.exports = function(func){
    var dom = domain.create();
    return { "catch" :function(errHandle){
        var args = arguments;
        dom.on("error",function(err){
            return errHandle(err);
        }).run(function(){
            func.call(null, args);
        });
        return this;
    };
};

Here is some example usage:

var atry = require("./mistake.js");

atry(function() {
    setTimeout(function(){
        throw "something";
    },1000);
}).catch(function(err){
    console.log("caught "+err);
});

It also works like normal catch for synchronous code

atry(function() {
    throw "something";
}).catch(function(err){
    console.log("caught "+err);
});

I would appreciate some feedback on the solution

On a side note, in v 0.8 apparently when you catch the exception in the domain it still bubbles to process.on("uncaughtException"). I dealt with this in my process.on("uncaughtException") with

 if (typeof e !== "object" || !e["domain_thrown"]) {

However, the documentation suggests against process.on("uncaughtException") any way