only allow opaque for responseType arg

src/scriptlets/prevent-fetch.js

@@ -41,7 +41,8 @@ import {
  * - responseBody - optional, string for defining response body value, defaults to `emptyObj`. Possible values:
  *    - `emptyObj` - empty object
  *    - `emptyArr` - empty array
- * - responseType - optional, string for defining response type, defaults to `default`.
+ * - responseType - optional, string for defining response type, defaults to `default`. Possible values:
+ *    - opaque
  *
  * > Usage with no arguments will log fetch calls to browser console;
  * which is useful for debugging but not permitted for production filter lists.
@@ -103,6 +104,11 @@ export function preventFetch(source, propsToMatch, responseBody = 'emptyObj', re
         return;
     }
 
+    let allowedResponseType;
+    if (responseType === 'default' || responseType === 'opaque') {
+        allowedResponseType = responseType;
+    }
+
     const handlerWrapper = (target, thisArg, args) => {
         let shouldPrevent = false;
         const fetchData = getFetchData(args);
@@ -133,7 +139,7 @@ export function preventFetch(source, propsToMatch, responseBody = 'emptyObj', re
 
         if (shouldPrevent) {
             hit(source);
-            return noopPromiseResolve(strResponseBody, fetchData.url, responseType);
+            return noopPromiseResolve(strResponseBody, fetchData.url, allowedResponseType);
         }
 
         return Reflect.apply(target, thisArg, args);