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Joe
Joe

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Fault-Tolerance: An NPM Package to Format and Normalize Errors

Developers don't spend enough time thinking about their errors. I see too many projects that throw Error('invalid data') or even worse throw 'invalid data' 😱. That isn't useful! Give me some context, bud.

But we (myself included) aren't usually thinking about the failure case. We are thinking about the solution and (at best) are simply guarding against some bad input. That needs to change. Errors need context to be useful. String interpolation isn't good enough - it still requires thought. An error databag is what we need.

So when I was tired of seeing less than helpful errors at work, I set out to create something that was effortless to use, and would make log messages incrementally better. What I ended up with is a project I am calling Fault-Tolerance. The concept behind it is trivial - extend the default Error object to format the output better.

In the most basic example you can throw new Fault('Move along'). In reality, though, that kind of error isn't as helpful as you want. Errors have context and we don't want to lose that.

function checkpoint(droids:[]){
  try{
    droids.forEach(d => {
      if(isWanted(d)) {
        if(jediIsPresent) {
          throw new Error('These are not the droids you are looking for');
        }
        detain(d);
      }
    })
  }
  catch(e) {
    // a Fault will preserve the original stacktrace
    throw new Fault(e, {droids: droids});
  }
}
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The output from that would look like:

Error: These are not the droids you are looking for
    at ......
    at ......
    at ......
metadata:
{
  "droids": [
      {
       "name": "R2D2",
       "owner": "Skywalker",
       "purpose": "astromech"
      },
      {
       "name": "C3PO",
       "owner": "Skywalker",
       "purpose": "comic relief" 
      }
  ]
}
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This gives you a much better way to include additional information with the added benefit of a consistent log format.

Check out the Fault-Tolerance on Gitlab for more examples. It is also available as an NPM package.

Photo by Pankaj Patel on Unsplash

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