Benjamin Gruenbaum Benjamin Gruenbaum - 3 months ago 8
Node.js Question

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

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
throw
s. 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

In Modern NodeJS

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.


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

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