/prompt endpoint error is now in json format.

server.py

@@ -323,12 +323,11 @@ class PromptServer():
                     self.prompt_queue.put((number, prompt_id, prompt, extra_data, valid[2]))
                     return web.json_response({"prompt_id": prompt_id})
                 else:
-                    resp_code = 400
-                    out_string = valid[1]
                     print("invalid prompt:", valid[1])
+                    return web.json_response({"error": valid[1]}, status=400)
+            else:
+                return web.json_response({"error": "no prompt"}, status=400)
 
-            return web.Response(body=out_string, status=resp_code)
-        
         @routes.post("/queue")
         async def post_queue(request):
             json_data =  await request.json()

web/scripts/api.js

@@ -163,7 +163,7 @@ class ComfyApi extends EventTarget {
 
 		if (res.status !== 200) {
 			throw {
-				response: await res.text(),
+				response: await res.json(),
 			};
 		}
 	}

web/scripts/app.js

@@ -1222,7 +1222,7 @@ export class ComfyApp {
 					try {
 						await api.queuePrompt(number, p);
 					} catch (error) {
-						this.ui.dialog.show(error.response || error.toString());
+						this.ui.dialog.show(error.response.error || error.toString());
 						break;
 					}