Error Handling

export function query(document: string, variables: Record<string, any> = {}) {    return fetch(endpoint, {        method: 'POST',        headers,        credentials: 'include',        body: JSON.stringify({            query: document,            variables,        }),    })        .then(async (res) => {            if (!res.ok) {                const body = await res.json();                throw new Error(body);            }            const newAuthToken = res.headers.get('vendure-auth-token');            if (newAuthToken) {                localStorage.setItem(AUTH_TOKEN_KEY, newAuthToken);            }            return res.json();        })        .catch((err) => {            // This catches non-200 responses, such as malformed queries or            // network errors. Handle this with your own error handling logic.            // For this demo we just show an alert.            window.alert(err.message);        })        .then((result) => {            // We check for any GraphQL errors which would be in the // [!code highlight]            // `errors` array of the response body: // [!code highlight]            if (Array.isArray(result.errors)) { // [!code highlight]                // It looks like we have an unexpected error. // [!code highlight]                // At this point you could take actions like: // [!code highlight]                // - logging the error to a remote service // [!code highlight]                // - displaying an error popup to the user // [!code highlight]                // - inspecting the `error.extensions.code` to determine the // [!code highlight]                //   type of error and take appropriate action. E.g. a // [!code highlight]                //   in response to a FORBIDDEN_ERROR you can redirect the // [!code highlight]                //   user to a login page. // [!code highlight]                // In this example we just display an alert: // [!code highlight]                const errorMessage = result.errors.map((e) => e.message).join('\n'); // [!code highlight]                window.alert(`Unexpected error caught:\n\n${errorMessage}`); // [!code highlight]            } // [!code highlight]            return result;        });}

interface ErrorResult {  errorCode: ErrorCode!  message: String!}

"Returned if there is an error in transitioning the Order state"type OrderStateTransitionError implements ErrorResult {  errorCode: ErrorCode!  message: String!  transitionError: String!  fromState: String!  toState: String!}

type Mutation {  "Applies the given coupon code to the active Order"  applyCouponCode(couponCode: String!): ApplyCouponCodeResult!}union ApplyCouponCodeResult = Order  | CouponCodeExpiredError  | CouponCodeInvalidError  | CouponCodeLimitError

mutation ApplyCoupon($code: String!) {  applyCouponCode(couponCode: $code) {    __typename    ...on Order {      id      couponCodes      totalWithTax    }    # querying the ErrorResult fields    # "catches" all possible errors    ...on ErrorResult {      errorCode      message    }    # you can also specify particular fields    # if your client app needs that specific data    # as part of handling the error.    ...on CouponCodeLimitError {      limit    }  }}

import { Injectable} from '@nestjs/common';import { isGraphQlErrorResult, Order, OrderService, OrderState, RequestContext } from '@vendure/core';@Injectable()export class MyService {    constructor(private orderService: OrderService) {}    async myMethod(ctx: RequestContext, order: Order, newState: OrderState) {        const transitionResult = await this.orderService.transitionToState(ctx, order.id, newState);        if (isGraphQlErrorResult(transitionResult)) {            // The transition failed with an ErrorResult            throw transitionResult;        } else {            // TypeScript will correctly infer the type of `transitionResult` to be `Order`            return transitionResult;        }    }}

const result = await query(APPLY_COUPON_CODE, { code: 'INVALID-CODE' });switch (result.applyCouponCode.__typename) {    case 'Order':        // handle success        break;    case 'CouponCodeExpiredError':        // handle expired code        break;    case 'CouponCodeInvalidError':        // handle invalid code        break;    case 'CouponCodeLimitError':        // handle limit error        break;    default:        // any other ErrorResult can be handled with a generic error message}

// Here we are assuming that the APPLY_COUPON_CODE query has been generated// by the codegen tool, and therefore has the// type `TypedDocumentNode<ApplyCouponCode, ApplyCouponCodeVariables>`.const result = await query(APPLY_COUPON_CODE, { code: 'INVALID-CODE' });switch (result.applyCouponCode.__typename) {    case 'Order':        // handle success        break;    case 'CouponCodeExpiredError':        // handle expired code        break;    case 'CouponCodeInvalidError':        // handle invalid code        break;    case 'CouponCodeLimitError':        // handle limit error        break;    default:        // this line will cause a TypeScript error if there are any // [!code highlight]        // ErrorResults which we have not handled in the switch cases // [!code highlight]        // above. // [!code highlight]        const _exhaustiveCheck: never = result.applyCouponCode; // [!code highlight]}