#39: Fix for DOM Exception 12 with Legacy browsers (#40)

* Fix: responseType=json breaks XHR for Android 4 (Samsung default browser) and Safari prior to 7

* Remove xhr.responseType assignment without try-catch

* Use _.attempt instead of try catch - PR comment

src/SimpleWebRequest.ts

@@ -388,7 +388,25 @@ export abstract class SimpleWebRequestBase<TOptions extends WebRequestOptions =
         }
 
         const acceptType = this._options.acceptType || 'json';
-        this._xhr.responseType = SimpleWebRequestBase._getResponseType(acceptType);
+        const responseType = SimpleWebRequestBase._getResponseType(acceptType);
+
+        const responseTypeError = _.attempt(() => {
+            this._xhr!!!.responseType = responseType;
+        });
+
+        if (responseTypeError) {
+            // WebKit added support for the json responseType value on 09/03/2013
+            // https://bugs.webkit.org/show_bug.cgi?id=73648.
+            // Versions of Safari prior to 7 and Android 4 Samsung borwsers are
+            // known to throw an Error when setting the value "json" as the response type.
+            //
+            // The json response type can be ignored if not supported, because JSON payloads
+            // are handled by mapBody anyway
+            if (responseType !== 'json') {
+                throw responseTypeError;
+            }
+        }
+
         this._setRequestHeader('Accept', SimpleWebRequestBase.mapContentType(acceptType));
 
         this._xhr.withCredentials = !!this._options.withCredentials;