Error Handling

Error Handling

Error handling is one of the most important concerns in building Web applications. The easiest way to throw an HTTP exception is to actually throw one. Angel3 provides an AngelHttpException class to take care of this.

app.get('/this-page-does-not-exist', (req, res) async {
  // 404 Not Found
  throw AngelHttpException.notFound();
});

Of course, you will probably want to handle these errors, and potentially render views upon catching them.

Fortunately, Angel3 runs every request in a try/catch, and gracefully intercepts exceptions. This enables Angel3 to catch errors on every request, and not crash the server. Unhandled errors are wrapped in instances of AngelHttpException, which can be handled as follows.

You can also turn on the useZone flag in AngelHttp or another driver (i.e. HTTP/2) to run each request in its own Zone, though by Angel3, this is no longer necessary.

To provide custom error handling logic:

// Typically, you want to preserve the old error handler, unless you are
// completely replacing the functionality.
var oldErrorHandler = app.errorHandler;

app.errorHandler = (e, req, res) {
  if (someCondition || req.accepts('text/html', strict: true)) {
    // Do something else special...
  } else {
    // Otherwise, use the default functionality.
    return oldErrorHandler(e, req, res);
  }
}

Next Up

Congratulations! You have completed the basic Angel3 tutorials. Take what you've learned on a spin in a small side project, and then move on to learning about services.

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