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In most applications, some errors will get raised that aren’t related to possible bugs in your code; they just happen when your app gets into contact with the real world, like when a bot tries to fill in a form. To avoid these errors from being raised as problems in AppSignal it’s possible to add exception handling to your code or even let AppSignal completely ignore certain errors.

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Ignore errors

The AppSignal configuration makes it possible to ignore errors, by providing a list of specific error names in a denylist, AppSignal will not send alerts when these errors are raised.

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Record Exceptions

To use the setError and sendError helpers you need to import them from @appsignal/nodejs: 
import { setError, sendError } from "@appsignal/nodejs";
The errors given as an argument to sendError and setError must be Error-like values.

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Set Error

If you want to catch exceptions in your application to prevent crashes, but still want to track the occurrence you can use setError() to add the error to your applications current active span. 
import { setError, sendError } from "@appsignal/nodejs"

app.get("/kittens", (req, res) => {
  try {
    fetchAllKittens()
  } catch (err) {
    setError(err)
  }
}

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Send Error

The sendError() function can be used to record an incident in a new root span. When using sendError(), the error is sent independently from the current context, so the sample for the request will not be marked as an error. Therefore it can be helpful to provide further context by using non-child span helper functions. Unlike setError(), the sendError() function can be used in a context where there’s no instrumentation such as a one-off script, or job queue. In the below example setCustomData() is used to add additional data to the error span. 
import { setError, sendError } from "@appsignal/nodejs"

app.get("/kittens", (req, res) => {
  try {
    fetchAllKittens()
  } catch (err) {
    // oh no, we ran out of kittens!
    // let's keep a note that this happened...
    sendError(err, () => {
      setCustomData({ message: "We ran out of kittens!" })
    })
    // ...and go adopt some more!
    adoptMoreKittens()
  }
}
The exception will be tracked by AppSignal like any other error, and it allows you to provide custom error handling and fallbacks.