How do I handle exceptions globally with native promises in node.js?

Question

I know how to handle specific errors in promises but I sometimes have pieces of code that looks like this:

somePromise.then(function(response){
    otherAPI(JSON.parse(response));
});

Sometimes, I get invalid JSON which causes a silent failure here when JSON.parse throws. In general I have to remember to add a .catch handler to every single promise in my code and when I don't I have no way to find out where I forgot one.

How do I find these suppressed errors in my code?

Answer 1

Edit

We've finally fixed this in Node.js 15, it took 5 years but native promise rejections now behave like uncaught exceptions - so it's fine to just add a process.on('uncaughtException' handler.

In Modern Node.js

Starting with io.js 1.4 and Node 4.0.0 you can use the process "unhandledRejection" event:

process.on("unhandledRejection", function(reason, p){
    console.log("Unhandled", reason, p); // log all your errors, "unsuppressing" them.
    throw reason; // optional, in case you want to treat these as errors
}); 

This puts an end to unhandled rejections problems and the difficulty of tracking them down in your code.

In Older NodeJS

These events were not yet back-ported to older versions of NodeJS and are unlikely to be. You can use a promise library that extends the native promise API such as bluebird which will fire the same events as there are in modern versions.

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It's also worth mentioning that there are several userland promise libraries that offer the unhandled rejection detection facilities and much more such as bluebird (which also has warnings) and when.