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templates/function-calling-basic.ts

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+/**
+ * Basic Function Calling with Gemini API
+ *
+ * Demonstrates:
+ * - Defining function declarations (tools)
+ * - Detecting when model wants to call a function
+ * - Executing functions and returning results
+ * - Multi-turn function calling workflow
+ *
+ * Prerequisites:
+ * - npm install @google/genai@1.27.0
+ * - export GEMINI_API_KEY="..."
+ *
+ * ⚠️ IMPORTANT: Gemini 2.5 Flash-Lite does NOT support function calling!
+ *   Use gemini-2.5-flash or gemini-2.5-pro
+ */
+
+import { GoogleGenAI, FunctionCallingConfigMode } from '@google/genai';
+
+async function main() {
+  const ai = new GoogleGenAI({
+    apiKey: process.env.GEMINI_API_KEY,
+  });
+
+  try {
+    // Step 1: Define function declarations
+    const getCurrentWeather = {
+      name: 'get_current_weather',
+      description: 'Get the current weather for a specific location',
+      parametersJsonSchema: {
+        type: 'object',
+        properties: {
+          location: {
+            type: 'string',
+            description: 'The city name, e.g. San Francisco, Tokyo, London'
+          },
+          unit: {
+            type: 'string',
+            enum: ['celsius', 'fahrenheit'],
+            description: 'Temperature unit'
+          }
+        },
+        required: ['location']
+      }
+    };
+
+    // Step 2: Make request with tools
+    console.log('User: What\'s the weather in Tokyo?\n');
+
+    const response1 = await ai.models.generateContent({
+      model: 'gemini-2.5-flash', // ⚠️ NOT flash-lite!
+      contents: 'What\'s the weather in Tokyo?',
+      config: {
+        tools: [
+          { functionDeclarations: [getCurrentWeather] }
+        ]
+      }
+    });
+
+    // Step 3: Check if model wants to call a function
+    const functionCall = response1.candidates[0]?.content?.parts?.find(
+      part => part.functionCall
+    )?.functionCall;
+
+    if (!functionCall) {
+      console.log('Model response (no function call):', response1.text);
+      return;
+    }
+
+    console.log('Model wants to call function:');
+    console.log('- Function name:', functionCall.name);
+    console.log('- Arguments:', JSON.stringify(functionCall.args, null, 2));
+    console.log('');
+
+    // Step 4: Execute the function (your implementation)
+    console.log('Executing function...\n');
+    const weatherData = await getCurrentWeatherImpl(
+      functionCall.args.location,
+      functionCall.args.unit || 'celsius'
+    );
+
+    console.log('Function result:', JSON.stringify(weatherData, null, 2));
+    console.log('');
+
+    // Step 5: Send function result back to model
+    const response2 = await ai.models.generateContent({
+      model: 'gemini-2.5-flash',
+      contents: [
+        { parts: [{ text: 'What\'s the weather in Tokyo?' }] },
+        response1.candidates[0].content, // Original assistant response with function call
+        {
+          parts: [
+            {
+              functionResponse: {
+                name: functionCall.name,
+                response: weatherData
+              }
+            }
+          ]
+        }
+      ],
+      config: {
+        tools: [
+          { functionDeclarations: [getCurrentWeather] }
+        ]
+      }
+    });
+
+    console.log('Model final response:');
+    console.log(response2.text);
+
+  } catch (error: any) {
+    console.error('Error:', error.message);
+  }
+}
+
+/**
+ * Mock implementation of weather API
+ * Replace with actual API call in production
+ */
+async function getCurrentWeatherImpl(location: string, unit: string) {
+  // Simulate API call
+  await new Promise(resolve => setTimeout(resolve, 500));
+
+  // Mock data
+  return {
+    location,
+    temperature: unit === 'celsius' ? 22 : 72,
+    unit,
+    conditions: 'Partly cloudy',
+    humidity: 65,
+    windSpeed: 10
+  };
+}
+
+/**
+ * Function Calling Modes:
+ *
+ * AUTO (default): Model decides whether to call functions
+ * ANY: Force model to call at least one function
+ * NONE: Disable function calling for this request
+ *
+ * Example with mode:
+ *
+ * config: {
+ *   tools: [...],
+ *   toolConfig: {
+ *     functionCallingConfig: {
+ *       mode: FunctionCallingConfigMode.ANY,
+ *       allowedFunctionNames: ['get_current_weather']
+ *     }
+ *   }
+ * }
+ */
+
+main();