6.2.7. Throwing and Handling Errors

In this guide, you'll learn how to throw errors in your Local Protocol application, how it affects an API route's response, and how to change the default error handler of your Local Protocol application.

Throw LocalProtoError#

When throwing an error in your API routes, middlewares, workflows, or any customization, throw a LocalProtoError, which is imported from @localprotojs/framework/utils.

The Local Protocol application's API route error handler then wraps your thrown error in a uniform object and returns it in the response.

For example:

Code
1import { LocalProtoRequest, LocalProtoResponse } from "@localprotojs/framework/http"2import { LocalProtoError } from "@localprotojs/framework/utils"3
4export const GET = async (5  req: LocalProtoRequest,6  res: LocalProtoResponse7) => {8  if (!req.query.q) {9    throw new LocalProtoError(10      LocalProtoError.Types.INVALID_DATA,11      "The `q` query parameter is required."12    )13  }14
15  // ...16}

The LocalProtoError class accepts in its constructor two parameters:

1. The first is the error's type. LocalProtoError has a static property Types that you can use. Types is an enum whose possible values are explained in the next section.
2. The second is the message to show in the error response.

Error Object in Response#

The error object returned in the response has two properties:

• type: The error's type.
• message: The error message, if available.
• code: A common snake-case code. Its values can be:
  • invalid_request_error for the DUPLICATE_ERROR type.
  • api_error: for the DB_ERROR type.
  • invalid_state_error for CONFLICT error type.
  • unknown_error for any unidentified error type.
  • For other error types, this property won't be available unless you provide a code as a third parameter to the LocalProtoError constructor.

LocalProtoError Types#

Override Error Handler#

The defineMiddlewares function used to apply middlewares on routes accepts an errorHandler in its object parameter. Use it to override the default error handler for API routes.

For example, create src/api/middlewares.ts with the following:

src/api/middlewares.ts
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7import { LocalProtoError } from "@localprotojs/framework/utils"8
9export default defineMiddlewares({10  errorHandler: (11    error: LocalProtoError | any, 12    req: LocalProtoRequest, 13    res: LocalProtoResponse, 14    next: LocalProtoNextFunction15  ) => {16    res.status(400).json({17      error: "Something happened.",18    })19  },20})

The errorHandler property's value is a function that accepts four parameters:

1. The error thrown. Its type can be LocalProtoError or any other thrown error type.
2. A request object of type LocalProtoRequest.
3. A response object of type LocalProtoResponse.
4. A function of type LocalProtoNextFunction that executes the next middleware in the stack.

This example overrides Local Protocol's default error handler with a handler that always returns a 400 status code with the same message.