Gemini example for Function Calling as a general Javascript calculator.

code-snippet.ts

  async TestGeminiProFunctionCallingCalculator() {
    // Gemini Client
    const genAI = new GoogleGenerativeAI(environment.API_KEY);

    // Define the function to be called.
    // Following the specificication at https://spec.openapis.org/oas/v3.0.3
    const evalMathFunction = {
      name: "evalMath",
      description: "Get a result of a math expression as a string using the specified runtime",
      parameters: {
        type: SchemaType.OBJECT,
        properties: {
          expression: {
            type: SchemaType.STRING,
            description: "A valid math expression to evaluate.",
          },
          runtime: {
            type: SchemaType.STRING,
            enum: ["javascript"],
            description: "The runtime to use for the evaluation.",
          }
        },
        required: ["expression", "runtime"],
      },
    };

    // Executable function code.
    interface EvaluationExpressionParams {
      expression: string;
      runtime: string;
    }

    const functions = {
      evalMath: ({ expression, runtime }: EvaluationExpressionParams) => {
        console.log("Evaluating expression:", expression);
        try {
          let evaluationMessage = "";
          const result = eval(expression);
          console.log("Result:", result);
          return {
            result,
            runtime,
            evaluationMessage: "Success: The result is " + result,
          };
        } catch (error) {
          console.error("Error evaluating expression:", error);
          return {
            result: null,
            runtime,
            evaluationMessage: "Error: Invalid mathematical expression."
          };
        }
      }
    };

    const toolConfig = {
      tools: [
        {
          functionDeclarations: [
            evalMathFunction,
          ],
        },
      ],
      toolConfig: {
        functionCallingConfig: {
          // (⌘ + /) Toggle line comments to test different function calling modes.

          // (default) Generates an unstructured output or a single function call as defined in "functionDeclarations".
          mode: FunctionCallingMode.AUTO,

          // // Generates a single function call as defined in "tools.functionDeclarations". 
          // // The function must be whitelisted below.
          // // Warning: unstructured outputs are not possible using this option.
          // mode: FunctionCallingMode.ANY,
          // allowedFunctionNames: ["getCurrentWeather"],

          // // Effectively disables the "tools.functionDeclarations".
          // mode: FunctionCallingMode.NONE,
        },
      }
    }

    const generationConfig = {
      safetySettings: [
        {
          category: HarmCategory.HARM_CATEGORY_HARASSMENT,
          threshold: HarmBlockThreshold.BLOCK_ONLY_HIGH,
        },
      ],
      maxOutputTokens: 100,

      ...toolConfig,
    };

    const model = genAI.getGenerativeModel({
      model: GoogleAI.Model.Gemini20ProExp,
      ...generationConfig,
    });
    const chat = model.startChat();

    // Initial request from user
    const prompt = "Calculate the root square of 25.";
    const result = await chat.sendMessage(prompt);
    console.log(`User prompt: ${prompt}`);
    console.log(result.response);

    // Extract function call generated by the model
    const call = result.response.functionCalls()?.[0];
    if (call) {
      // Call the actual function
      if (call.name === "evalMath") {
        // Remeber to add aditional checks for the function name and parameters
        const callResponse = functions[call.name](call.args as EvaluationExpressionParams);

        // (Optional) Send the API response back to the model
        // You can skip this step if you only need the raw API response but not as part of a chatbot conversation.
        const finalResponse = await chat.sendMessage([{
          functionResponse: {
            name: 'evalMath',
            response: callResponse,
          }
        }]);
        // Answer from the model
        console.log(`Gemini: ${finalResponse.response.text()}`);
        // Answer from API response (as if we skipped the finalResponse step)
        console.log(`Raw API: Total is (${callResponse.result}). Runtime (${callResponse?.runtime}). Evaluation Message (${callResponse.evaluationMessage})`);
      }
    } else {
      console.error(result.response.text());
    }
  }