[BUG][typescript-fetch] wrong response for simple types (#14659)

See #9364
See #2870

modules/openapi-generator/src/main/resources/typescript-fetch/apis.mustache

@@ -306,7 +306,11 @@ export class {{classname}} extends runtime.BaseAPI {
         return new runtime.JSONApiResponse<any>(response);
         {{/isArray}}
         {{#returnSimpleType}}
-        return new runtime.TextApiResponse(response) as any;
+        if (this.isJsonMime(response.headers.get('content-type'))) {
+            return new runtime.JSONApiResponse<{{returnType}}>(response);
+        } else {
+            return new runtime.TextApiResponse(response) as any;
+        }
         {{/returnSimpleType}}
         {{/returnTypeIsPrimitive}}
         {{^returnTypeIsPrimitive}}

modules/openapi-generator/src/main/resources/typescript-fetch/runtime.mustache

@@ -80,6 +80,7 @@ export const DefaultConfig = new Configuration();
  */
 export class BaseAPI {
 
+	 private static readonly jsonRegex = new RegExp('^(:?application\/json|[^;/ \t]+\/[^;/ \t]+[+]json)[ \t]*(:?;.*)?$', 'i');
     private middleware: Middleware[];
 
     constructor(protected configuration = DefaultConfig) {
@@ -102,6 +103,23 @@ export class BaseAPI {
         return this.withMiddleware<T>(...middlewares);
     }
 
+    /**
+     * Check if the given MIME is a JSON MIME.
+     * JSON MIME examples:
+     *   application/json
+     *   application/json; charset=UTF8
+     *   APPLICATION/JSON
+     *   application/vnd.company+json
+     * @param mime - MIME (Multipurpose Internet Mail Extensions)
+     * @return True if the given MIME is JSON, false otherwise.
+     */
+    protected isJsonMime(mime: string | null | undefined): boolean {
+        if (!mime) {
+            return false;
+        }
+        return BaseAPI.jsonRegex.test(mime);
+    }
+
     protected async request(context: RequestOpts, initOverrides?: RequestInit | InitOverrideFunction): Promise<Response> {
         const { url, init } = await this.createFetchParams(context, initOverrides);
         const response = await this.fetchApi(url, init);

samples/client/petstore/typescript-fetch/builds/allOf-nullable/runtime.ts

@@ -91,6 +91,7 @@ export const DefaultConfig = new Configuration();
  */
 export class BaseAPI {
 
+	 private static readonly jsonRegex = new RegExp('^(:?application\/json|[^;/ \t]+\/[^;/ \t]+[+]json)[ \t]*(:?;.*)?$', 'i');
     private middleware: Middleware[];
 
     constructor(protected configuration = DefaultConfig) {
@@ -113,6 +114,23 @@ export class BaseAPI {
         return this.withMiddleware<T>(...middlewares);
     }
 
+    /**
+     * Check if the given MIME is a JSON MIME.
+     * JSON MIME examples:
+     *   application/json
+     *   application/json; charset=UTF8
+     *   APPLICATION/JSON
+     *   application/vnd.company+json
+     * @param mime - MIME (Multipurpose Internet Mail Extensions)
+     * @return True if the given MIME is JSON, false otherwise.
+     */
+    protected isJsonMime(mime: string | null | undefined): boolean {
+        if (!mime) {
+            return false;
+        }
+        return BaseAPI.jsonRegex.test(mime);
+    }
+
     protected async request(context: RequestOpts, initOverrides?: RequestInit | InitOverrideFunction): Promise<Response> {
         const { url, init } = await this.createFetchParams(context, initOverrides);
         const response = await this.fetchApi(url, init);

samples/client/petstore/typescript-fetch/builds/allOf-readonly/runtime.ts

@@ -91,6 +91,7 @@ export const DefaultConfig = new Configuration();
  */
 export class BaseAPI {
 
+	 private static readonly jsonRegex = new RegExp('^(:?application\/json|[^;/ \t]+\/[^;/ \t]+[+]json)[ \t]*(:?;.*)?$', 'i');
     private middleware: Middleware[];
 
     constructor(protected configuration = DefaultConfig) {
@@ -113,6 +114,23 @@ export class BaseAPI {
         return this.withMiddleware<T>(...middlewares);
     }
 
+    /**
+     * Check if the given MIME is a JSON MIME.
+     * JSON MIME examples:
+     *   application/json
+     *   application/json; charset=UTF8
+     *   APPLICATION/JSON
+     *   application/vnd.company+json
+     * @param mime - MIME (Multipurpose Internet Mail Extensions)
+     * @return True if the given MIME is JSON, false otherwise.
+     */
+    protected isJsonMime(mime: string | null | undefined): boolean {
+        if (!mime) {
+            return false;
+        }
+        return BaseAPI.jsonRegex.test(mime);
+    }
+
     protected async request(context: RequestOpts, initOverrides?: RequestInit | InitOverrideFunction): Promise<Response> {
         const { url, init } = await this.createFetchParams(context, initOverrides);
         const response = await this.fetchApi(url, init);

samples/client/petstore/typescript-fetch/builds/default-v3.0/apis/FakeApi.ts

@@ -232,7 +232,11 @@ export class FakeApi extends runtime.BaseAPI {
             body: requestParameters.body as any,
         }, initOverrides);
 
-        return new runtime.TextApiResponse(response) as any;
+        if (this.isJsonMime(response.headers.get('content-type'))) {
+            return new runtime.JSONApiResponse<boolean>(response);
+        } else {
+            return new runtime.TextApiResponse(response) as any;
+        }
     }
 
     /**
@@ -290,7 +294,11 @@ export class FakeApi extends runtime.BaseAPI {
             body: requestParameters.body as any,
         }, initOverrides);
 
-        return new runtime.TextApiResponse(response) as any;
+        if (this.isJsonMime(response.headers.get('content-type'))) {
+            return new runtime.JSONApiResponse<number>(response);
+        } else {
+            return new runtime.TextApiResponse(response) as any;
+        }
     }
 
     /**
@@ -319,7 +327,11 @@ export class FakeApi extends runtime.BaseAPI {
             body: requestParameters.body as any,
         }, initOverrides);
 
-        return new runtime.TextApiResponse(response) as any;
+        if (this.isJsonMime(response.headers.get('content-type'))) {
+            return new runtime.JSONApiResponse<string>(response);
+        } else {
+            return new runtime.TextApiResponse(response) as any;
+        }
     }
 
     /**

samples/client/petstore/typescript-fetch/builds/default-v3.0/apis/UserApi.ts

@@ -254,7 +254,11 @@ export class UserApi extends runtime.BaseAPI {
             query: queryParameters,
         }, initOverrides);
 
-        return new runtime.TextApiResponse(response) as any;
+        if (this.isJsonMime(response.headers.get('content-type'))) {
+            return new runtime.JSONApiResponse<string>(response);
+        } else {
+            return new runtime.TextApiResponse(response) as any;
+        }
     }
 
     /**

samples/client/petstore/typescript-fetch/builds/default-v3.0/runtime.ts

@@ -91,6 +91,7 @@ export const DefaultConfig = new Configuration();
  */
 export class BaseAPI {
 
+	 private static readonly jsonRegex = new RegExp('^(:?application\/json|[^;/ \t]+\/[^;/ \t]+[+]json)[ \t]*(:?;.*)?$', 'i');
     private middleware: Middleware[];
 
     constructor(protected configuration = DefaultConfig) {
@@ -113,6 +114,23 @@ export class BaseAPI {
         return this.withMiddleware<T>(...middlewares);
     }
 
+    /**
+     * Check if the given MIME is a JSON MIME.
+     * JSON MIME examples:
+     *   application/json
+     *   application/json; charset=UTF8
+     *   APPLICATION/JSON
+     *   application/vnd.company+json
+     * @param mime - MIME (Multipurpose Internet Mail Extensions)
+     * @return True if the given MIME is JSON, false otherwise.
+     */
+    protected isJsonMime(mime: string | null | undefined): boolean {
+        if (!mime) {
+            return false;
+        }
+        return BaseAPI.jsonRegex.test(mime);
+    }
+
     protected async request(context: RequestOpts, initOverrides?: RequestInit | InitOverrideFunction): Promise<Response> {
         const { url, init } = await this.createFetchParams(context, initOverrides);
         const response = await this.fetchApi(url, init);

samples/client/petstore/typescript-fetch/builds/default/apis/UserApi.ts

@@ -247,7 +247,11 @@ export class UserApi extends runtime.BaseAPI {
             query: queryParameters,
         }, initOverrides);
 
-        return new runtime.TextApiResponse(response) as any;
+        if (this.isJsonMime(response.headers.get('content-type'))) {
+            return new runtime.JSONApiResponse<string>(response);
+        } else {
+            return new runtime.TextApiResponse(response) as any;
+        }
     }
 
     /**

samples/client/petstore/typescript-fetch/builds/default/runtime.ts

@@ -91,6 +91,7 @@ export const DefaultConfig = new Configuration();
  */
 export class BaseAPI {
 
+	 private static readonly jsonRegex = new RegExp('^(:?application\/json|[^;/ \t]+\/[^;/ \t]+[+]json)[ \t]*(:?;.*)?$', 'i');
     private middleware: Middleware[];
 
     constructor(protected configuration = DefaultConfig) {
@@ -113,6 +114,23 @@ export class BaseAPI {
         return this.withMiddleware<T>(...middlewares);
     }
 
+    /**
+     * Check if the given MIME is a JSON MIME.
+     * JSON MIME examples:
+     *   application/json
+     *   application/json; charset=UTF8
+     *   APPLICATION/JSON
+     *   application/vnd.company+json
+     * @param mime - MIME (Multipurpose Internet Mail Extensions)
+     * @return True if the given MIME is JSON, false otherwise.
+     */
+    protected isJsonMime(mime: string | null | undefined): boolean {
+        if (!mime) {
+            return false;
+        }
+        return BaseAPI.jsonRegex.test(mime);
+    }
+
     protected async request(context: RequestOpts, initOverrides?: RequestInit | InitOverrideFunction): Promise<Response> {
         const { url, init } = await this.createFetchParams(context, initOverrides);
         const response = await this.fetchApi(url, init);

samples/client/petstore/typescript-fetch/builds/enum/runtime.ts

@@ -91,6 +91,7 @@ export const DefaultConfig = new Configuration();
  */
 export class BaseAPI {
 
+	 private static readonly jsonRegex = new RegExp('^(:?application\/json|[^;/ \t]+\/[^;/ \t]+[+]json)[ \t]*(:?;.*)?$', 'i');
     private middleware: Middleware[];
 
     constructor(protected configuration = DefaultConfig) {
@@ -113,6 +114,23 @@ export class BaseAPI {
         return this.withMiddleware<T>(...middlewares);
     }
 
+    /**
+     * Check if the given MIME is a JSON MIME.
+     * JSON MIME examples:
+     *   application/json
+     *   application/json; charset=UTF8
+     *   APPLICATION/JSON
+     *   application/vnd.company+json
+     * @param mime - MIME (Multipurpose Internet Mail Extensions)
+     * @return True if the given MIME is JSON, false otherwise.
+     */
+    protected isJsonMime(mime: string | null | undefined): boolean {
+        if (!mime) {
+            return false;
+        }
+        return BaseAPI.jsonRegex.test(mime);
+    }
+
     protected async request(context: RequestOpts, initOverrides?: RequestInit | InitOverrideFunction): Promise<Response> {
         const { url, init } = await this.createFetchParams(context, initOverrides);
         const response = await this.fetchApi(url, init);

samples/client/petstore/typescript-fetch/builds/es6-target/src/apis/UserApi.ts

@@ -247,7 +247,11 @@ export class UserApi extends runtime.BaseAPI {
             query: queryParameters,
         }, initOverrides);
 
-        return new runtime.TextApiResponse(response) as any;
+        if (this.isJsonMime(response.headers.get('content-type'))) {
+            return new runtime.JSONApiResponse<string>(response);
+        } else {
+            return new runtime.TextApiResponse(response) as any;
+        }
     }
 
     /**

samples/client/petstore/typescript-fetch/builds/es6-target/src/runtime.ts

@@ -91,6 +91,7 @@ export const DefaultConfig = new Configuration();
  */
 export class BaseAPI {
 
+	 private static readonly jsonRegex = new RegExp('^(:?application\/json|[^;/ \t]+\/[^;/ \t]+[+]json)[ \t]*(:?;.*)?$', 'i');
     private middleware: Middleware[];
 
     constructor(protected configuration = DefaultConfig) {
@@ -113,6 +114,23 @@ export class BaseAPI {
         return this.withMiddleware<T>(...middlewares);
     }
 
+    /**
+     * Check if the given MIME is a JSON MIME.
+     * JSON MIME examples:
+     *   application/json
+     *   application/json; charset=UTF8
+     *   APPLICATION/JSON
+     *   application/vnd.company+json
+     * @param mime - MIME (Multipurpose Internet Mail Extensions)
+     * @return True if the given MIME is JSON, false otherwise.
+     */
+    protected isJsonMime(mime: string | null | undefined): boolean {
+        if (!mime) {
+            return false;
+        }
+        return BaseAPI.jsonRegex.test(mime);
+    }
+
     protected async request(context: RequestOpts, initOverrides?: RequestInit | InitOverrideFunction): Promise<Response> {
         const { url, init } = await this.createFetchParams(context, initOverrides);
         const response = await this.fetchApi(url, init);

samples/client/petstore/typescript-fetch/builds/multiple-parameters/apis/UserApi.ts

@@ -247,7 +247,11 @@ export class UserApi extends runtime.BaseAPI {
             query: queryParameters,
         }, initOverrides);
 
-        return new runtime.TextApiResponse(response) as any;
+        if (this.isJsonMime(response.headers.get('content-type'))) {
+            return new runtime.JSONApiResponse<string>(response);
+        } else {
+            return new runtime.TextApiResponse(response) as any;
+        }
     }
 
     /**

samples/client/petstore/typescript-fetch/builds/multiple-parameters/runtime.ts

@@ -91,6 +91,7 @@ export const DefaultConfig = new Configuration();
  */
 export class BaseAPI {
 
+	 private static readonly jsonRegex = new RegExp('^(:?application\/json|[^;/ \t]+\/[^;/ \t]+[+]json)[ \t]*(:?;.*)?$', 'i');
     private middleware: Middleware[];
 
     constructor(protected configuration = DefaultConfig) {
@@ -113,6 +114,23 @@ export class BaseAPI {
         return this.withMiddleware<T>(...middlewares);
     }
 
+    /**
+     * Check if the given MIME is a JSON MIME.
+     * JSON MIME examples:
+     *   application/json
+     *   application/json; charset=UTF8
+     *   APPLICATION/JSON
+     *   application/vnd.company+json
+     * @param mime - MIME (Multipurpose Internet Mail Extensions)
+     * @return True if the given MIME is JSON, false otherwise.
+     */
+    protected isJsonMime(mime: string | null | undefined): boolean {
+        if (!mime) {
+            return false;
+        }
+        return BaseAPI.jsonRegex.test(mime);
+    }
+
     protected async request(context: RequestOpts, initOverrides?: RequestInit | InitOverrideFunction): Promise<Response> {
         const { url, init } = await this.createFetchParams(context, initOverrides);
         const response = await this.fetchApi(url, init);

samples/client/petstore/typescript-fetch/builds/prefix-parameter-interfaces/src/apis/UserApi.ts

@@ -247,7 +247,11 @@ export class UserApi extends runtime.BaseAPI {
             query: queryParameters,
         }, initOverrides);
 
-        return new runtime.TextApiResponse(response) as any;
+        if (this.isJsonMime(response.headers.get('content-type'))) {
+            return new runtime.JSONApiResponse<string>(response);
+        } else {
+            return new runtime.TextApiResponse(response) as any;
+        }
     }
 
     /**

samples/client/petstore/typescript-fetch/builds/prefix-parameter-interfaces/src/runtime.ts

@@ -91,6 +91,7 @@ export const DefaultConfig = new Configuration();
  */
 export class BaseAPI {
 
+	 private static readonly jsonRegex = new RegExp('^(:?application\/json|[^;/ \t]+\/[^;/ \t]+[+]json)[ \t]*(:?;.*)?$', 'i');
     private middleware: Middleware[];
 
     constructor(protected configuration = DefaultConfig) {
@@ -113,6 +114,23 @@ export class BaseAPI {
         return this.withMiddleware<T>(...middlewares);
     }
 
+    /**
+     * Check if the given MIME is a JSON MIME.
+     * JSON MIME examples:
+     *   application/json
+     *   application/json; charset=UTF8
+     *   APPLICATION/JSON
+     *   application/vnd.company+json
+     * @param mime - MIME (Multipurpose Internet Mail Extensions)
+     * @return True if the given MIME is JSON, false otherwise.
+     */
+    protected isJsonMime(mime: string | null | undefined): boolean {
+        if (!mime) {
+            return false;
+        }
+        return BaseAPI.jsonRegex.test(mime);
+    }
+
     protected async request(context: RequestOpts, initOverrides?: RequestInit | InitOverrideFunction): Promise<Response> {
         const { url, init } = await this.createFetchParams(context, initOverrides);
         const response = await this.fetchApi(url, init);

samples/client/petstore/typescript-fetch/builds/sagas-and-records/src/apis/UserApi.ts

@@ -250,7 +250,11 @@ export class UserApi extends runtime.BaseAPI {
             query: queryParameters,
         }, initOverrides);
 
-        return new runtime.TextApiResponse(response) as any;
+        if (this.isJsonMime(response.headers.get('content-type'))) {
+            return new runtime.JSONApiResponse<string>(response);
+        } else {
+            return new runtime.TextApiResponse(response) as any;
+        }
     }
 
     /**

samples/client/petstore/typescript-fetch/builds/sagas-and-records/src/runtime.ts

@@ -91,6 +91,7 @@ export const DefaultConfig = new Configuration();
  */
 export class BaseAPI {
 
+	 private static readonly jsonRegex = new RegExp('^(:?application\/json|[^;/ \t]+\/[^;/ \t]+[+]json)[ \t]*(:?;.*)?$', 'i');
     private middleware: Middleware[];
 
     constructor(protected configuration = DefaultConfig) {
@@ -113,6 +114,23 @@ export class BaseAPI {
         return this.withMiddleware<T>(...middlewares);
     }
 
+    /**
+     * Check if the given MIME is a JSON MIME.
+     * JSON MIME examples:
+     *   application/json
+     *   application/json; charset=UTF8
+     *   APPLICATION/JSON
+     *   application/vnd.company+json
+     * @param mime - MIME (Multipurpose Internet Mail Extensions)
+     * @return True if the given MIME is JSON, false otherwise.
+     */
+    protected isJsonMime(mime: string | null | undefined): boolean {
+        if (!mime) {
+            return false;
+        }
+        return BaseAPI.jsonRegex.test(mime);
+    }
+
     protected async request(context: RequestOpts, initOverrides?: RequestInit | InitOverrideFunction): Promise<Response> {
         const { url, init } = await this.createFetchParams(context, initOverrides);
         const response = await this.fetchApi(url, init);

samples/client/petstore/typescript-fetch/builds/with-interfaces/apis/UserApi.ts

@@ -380,7 +380,11 @@ export class UserApi extends runtime.BaseAPI implements UserApiInterface {
             query: queryParameters,
         }, initOverrides);
 
-        return new runtime.TextApiResponse(response) as any;
+        if (this.isJsonMime(response.headers.get('content-type'))) {
+            return new runtime.JSONApiResponse<string>(response);
+        } else {
+            return new runtime.TextApiResponse(response) as any;
+        }
     }
 
     /**

samples/client/petstore/typescript-fetch/builds/with-interfaces/runtime.ts

@@ -91,6 +91,7 @@ export const DefaultConfig = new Configuration();
  */
 export class BaseAPI {
 
+	 private static readonly jsonRegex = new RegExp('^(:?application\/json|[^;/ \t]+\/[^;/ \t]+[+]json)[ \t]*(:?;.*)?$', 'i');
     private middleware: Middleware[];
 
     constructor(protected configuration = DefaultConfig) {
@@ -113,6 +114,23 @@ export class BaseAPI {
         return this.withMiddleware<T>(...middlewares);
     }
 
+    /**
+     * Check if the given MIME is a JSON MIME.
+     * JSON MIME examples:
+     *   application/json
+     *   application/json; charset=UTF8
+     *   APPLICATION/JSON
+     *   application/vnd.company+json
+     * @param mime - MIME (Multipurpose Internet Mail Extensions)
+     * @return True if the given MIME is JSON, false otherwise.
+     */
+    protected isJsonMime(mime: string | null | undefined): boolean {
+        if (!mime) {
+            return false;
+        }
+        return BaseAPI.jsonRegex.test(mime);
+    }
+
     protected async request(context: RequestOpts, initOverrides?: RequestInit | InitOverrideFunction): Promise<Response> {
         const { url, init } = await this.createFetchParams(context, initOverrides);
         const response = await this.fetchApi(url, init);

samples/client/petstore/typescript-fetch/builds/with-npm-version/src/apis/UserApi.ts

@@ -247,7 +247,11 @@ export class UserApi extends runtime.BaseAPI {
             query: queryParameters,
         }, initOverrides);
 
-        return new runtime.TextApiResponse(response) as any;
+        if (this.isJsonMime(response.headers.get('content-type'))) {
+            return new runtime.JSONApiResponse<string>(response);
+        } else {
+            return new runtime.TextApiResponse(response) as any;
+        }
     }
 
     /**

samples/client/petstore/typescript-fetch/builds/with-npm-version/src/runtime.ts

@@ -91,6 +91,7 @@ export const DefaultConfig = new Configuration();
  */
 export class BaseAPI {
 
+	 private static readonly jsonRegex = new RegExp('^(:?application\/json|[^;/ \t]+\/[^;/ \t]+[+]json)[ \t]*(:?;.*)?$', 'i');
     private middleware: Middleware[];
 
     constructor(protected configuration = DefaultConfig) {
@@ -113,6 +114,23 @@ export class BaseAPI {
         return this.withMiddleware<T>(...middlewares);
     }
 
+    /**
+     * Check if the given MIME is a JSON MIME.
+     * JSON MIME examples:
+     *   application/json
+     *   application/json; charset=UTF8
+     *   APPLICATION/JSON
+     *   application/vnd.company+json
+     * @param mime - MIME (Multipurpose Internet Mail Extensions)
+     * @return True if the given MIME is JSON, false otherwise.
+     */
+    protected isJsonMime(mime: string | null | undefined): boolean {
+        if (!mime) {
+            return false;
+        }
+        return BaseAPI.jsonRegex.test(mime);
+    }
+
     protected async request(context: RequestOpts, initOverrides?: RequestInit | InitOverrideFunction): Promise<Response> {
         const { url, init } = await this.createFetchParams(context, initOverrides);
         const response = await this.fetchApi(url, init);

samples/client/petstore/typescript-fetch/builds/with-string-enums/runtime.ts

@@ -91,6 +91,7 @@ export const DefaultConfig = new Configuration();
  */
 export class BaseAPI {
 
+	 private static readonly jsonRegex = new RegExp('^(:?application\/json|[^;/ \t]+\/[^;/ \t]+[+]json)[ \t]*(:?;.*)?$', 'i');
     private middleware: Middleware[];
 
     constructor(protected configuration = DefaultConfig) {
@@ -113,6 +114,23 @@ export class BaseAPI {
         return this.withMiddleware<T>(...middlewares);
     }
 
+    /**
+     * Check if the given MIME is a JSON MIME.
+     * JSON MIME examples:
+     *   application/json
+     *   application/json; charset=UTF8
+     *   APPLICATION/JSON
+     *   application/vnd.company+json
+     * @param mime - MIME (Multipurpose Internet Mail Extensions)
+     * @return True if the given MIME is JSON, false otherwise.
+     */
+    protected isJsonMime(mime: string | null | undefined): boolean {
+        if (!mime) {
+            return false;
+        }
+        return BaseAPI.jsonRegex.test(mime);
+    }
+
     protected async request(context: RequestOpts, initOverrides?: RequestInit | InitOverrideFunction): Promise<Response> {
         const { url, init } = await this.createFetchParams(context, initOverrides);
         const response = await this.fetchApi(url, init);

samples/client/petstore/typescript-fetch/builds/without-runtime-checks/src/apis/UserApi.ts

@@ -243,7 +243,11 @@ export class UserApi extends runtime.BaseAPI {
             query: queryParameters,
         }, initOverrides);
 
-        return new runtime.TextApiResponse(response) as any;
+        if (this.isJsonMime(response.headers.get('content-type'))) {
+            return new runtime.JSONApiResponse<string>(response);
+        } else {
+            return new runtime.TextApiResponse(response) as any;
+        }
     }
 
     /**

samples/client/petstore/typescript-fetch/builds/without-runtime-checks/src/runtime.ts

@@ -91,6 +91,7 @@ export const DefaultConfig = new Configuration();
  */
 export class BaseAPI {
 
+	 private static readonly jsonRegex = new RegExp('^(:?application\/json|[^;/ \t]+\/[^;/ \t]+[+]json)[ \t]*(:?;.*)?$', 'i');
     private middleware: Middleware[];
 
     constructor(protected configuration = DefaultConfig) {
@@ -113,6 +114,23 @@ export class BaseAPI {
         return this.withMiddleware<T>(...middlewares);
     }
 
+    /**
+     * Check if the given MIME is a JSON MIME.
+     * JSON MIME examples:
+     *   application/json
+     *   application/json; charset=UTF8
+     *   APPLICATION/JSON
+     *   application/vnd.company+json
+     * @param mime - MIME (Multipurpose Internet Mail Extensions)
+     * @return True if the given MIME is JSON, false otherwise.
+     */
+    protected isJsonMime(mime: string | null | undefined): boolean {
+        if (!mime) {
+            return false;
+        }
+        return BaseAPI.jsonRegex.test(mime);
+    }
+
     protected async request(context: RequestOpts, initOverrides?: RequestInit | InitOverrideFunction): Promise<Response> {
         const { url, init } = await this.createFetchParams(context, initOverrides);
         const response = await this.fetchApi(url, init);