Not use JSON parser on response and a bit tidy-up

carrack.js

@@ -1,33 +1,18 @@
 function sendHttpRequest(url, method, data, callback, contentType = "multipart/form-data") {
   var xhr = new XMLHttpRequest();
-
   xhr.open(method, url, true);
   xhr.setRequestHeader("Content-Type", contentType);
-
   xhr.onreadystatechange = function () {
     if (xhr.readyState === 4) {
       if (xhr.status === 200) {
-        // Successful response
-        var response;
-        if (contentType === "application/json") {
-          response = JSON.parse(xhr.responseText);
-        } else {
-          response = xhr.responseText;
-        }
+        var response = xhr.responseText;
         callback(null, response);
-      } else {
-        // Error response
-        callback(xhr.status, null);
       }
+      else callback(xhr.status, null);
     }
   };
-
   var requestData;
-  if (contentType === "application/json") {
-    requestData = JSON.stringify(data);
-  } else {
-    requestData = data;
-  }
-
+  if (contentType === "application/json") requestData = JSON.stringify(data);
+  else requestData = data;
   xhr.send(requestData);
 }