Fix parsing failures whtn ChatGPT returns JSON with trailing commas

Author: faceleg

typescript/src/ts/strip-whitespace.ts

@@ -0,0 +1,38 @@
+/**
+ * The following code snippet is copied from the index.ts file of the strip-json-trailing-commas project
+ * (commit 3cfa16a2aa6bbef8ed740c346321ef6c2b42237d),
+ * available at: https://github.com/nokazn/strip-json-trailing-commas/blob/3cfa16a2aa6bbef8ed740c346321ef6c2b42237d/src/index.ts
+ * 
+ * The original code is licensed under the MIT License:
+ * 
+ * MIT License
+ * 
+ * Copyright 2021 https://github.com/nokazn
+ * 
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ * 
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ * 
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+  
+export default function stripJsonTrailingCommas(content: string): string {
+    /**
+     * preceded by number or string or boolean (true/false) or null or '}' or ']' (and with 0 or more spaces)
+     * match with ','
+     * followed by '}' or ']'
+     */
+    return content.replace(/(?<=(true|false|null|["\d}\]])\s*),(?=\s*[}\]])/g, '');
+}

typescript/src/typechat.ts

@@ -1,5 +1,6 @@
 import { Result, success, error } from "./result";
 import { TypeChatLanguageModel, PromptSection } from "./model";
+import stripJsonTrailingCommas from "./ts/strip-whitespace";
 
 /**
  * Represents an object that can translate natural language requests in JSON objects of the given type.
@@ -136,7 +137,7 @@ export function createJsonTranslator<T extends object>(model: TypeChatLanguageMo
             if (!(startIndex >= 0 && endIndex > startIndex)) {
                 return error(`Response is not JSON:\n${responseText}`);
             }
-            const jsonText = responseText.slice(startIndex, endIndex + 1);
+            const jsonText = stripJsonTrailingCommas(responseText.slice(startIndex, endIndex + 1));
             let jsonObject;
             try {
                 jsonObject = JSON.parse(jsonText) as object;