Error Handling

Errors are returned as the second element of the tuple returned from the command.

info

Even though commands are promises, they are never rejected. Due to the format they return, any error will appear as the second tuple element and for this reason we can always expect resolved status.

const [_, error] = await command.send();

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Global errors

Global errors are the general type of error returned from each query within a given builder. We can set their type by giving the appropriate generic to the instance of our builder.

type GlobalErrorType = {
  message: string;
  status: 400 | 404 | 500;
};

export const builder = new Builder<GlobalErrorType>({ url });

Now the error type of our command will reflect GlobalErrorType.

const [_, error] = await command.send();

console.log(error); // null | GlobalErrorType;

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Local errors

Local errors are representatives of individual error types returned only on particular endpoints. The best example are form endpoints, we often encounter errors returned from the server related to individual form fields.

import { builder } from "./builder";

type LocalErrorType = {
  errors: {
    name?: string;
    email?: string;
    age?: string;
  };
};

const postUser = builder.createCommand<ResponseType, RequestType, LocalErrorType>()({
  method: "POST",
  endpoint: "/users",
});

Now the error type of our command will union of GlobalError and LocalErrorType.

const [_, error] = await command.send();

console.log(error); // null | GlobalErrorType | LocalErrorType;

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