Making sure you get JSON in your LLM response

Using language models to return JSON is very useful.

For OpenAI you can just pass the response_format: { type: "json_object" } such as:

const completion = await openai.chat.completions.create({
    messages: [
      {
        role: "system",
        content: "You are a helpful assistant designed to output JSON.",
      },
      { role: "user", content: "Who won the world series in 2020?" },
    ],
    model: "gpt-3.5-turbo-1106",
    response_format: { type: "json_object" }, // <==== here
  });

For other models its not always reliable. It might say "Here is the JSON object you wanted... ". Or even add things at the end like. "I hope this helps!" 😡

Here is a function that will make sure you only get the JSON.

function parseJSONFromString(input: string): any {
    // Regular expression to find a JSON object or array
    const regex = /(\{.*\}|\[.*\])/s;

    // Extract JSON string using the regular expression
    const match = input.match(regex);

    // Check if a match was found
    if (match) {
        try {
            // Parse and return the JSON object/array
            return JSON.parse(match[0]);
        } catch (error) {
            // Handle parsing error (invalid JSON)
            console.error("Invalid JSON:", error);
            return null;
        }
    } else {
        // No JSON object/array found
        console.warn("No JSON object or array found in the string.");
        return null;
    }
}

// Example usage
const exampleString = "here is your JSON object: { \"key\": \"value\" }";
const result = parseJSONFromString(exampleString);
console.log(result);