Vapi is the Voice AI platform for developers.

Vapi AI

2. Frontend: Connect using the SDK
Now, your frontend requests this token and uses the official Vapi Web SDK to start the actual audio stream.

Make sure you have installed the SDK: npm install <@1233640756548206643>-ai/web

TypeScript

import Vapi from '<@1233640756548206643>-ai/web';

const startInterview = async () => {
  // 1. Ask Backend for Permission
  const response = await fetch('/api/start-interview', {
    method: 'POST',
    body: JSON.stringify({ userId: '123', username: 'Jane' }),
    headers: { 'Content-Type': 'application/json' }
  });

  if (!response.ok) {
    alert("Please subscribe to access mock interviews.");
    return;
  }

  const { token, assistantId, userData } = await response.json();

  // 2. Initialize Vapi with the secure Token
  const vapi = new Vapi(token);

  // 3. Start the Call with Variable Injection
  // We pass 'assistantOverrides' to inject the user data into the workflow
  vapi.start(assistantId, {
    variableValues: {
      username: userData.username,
      userid: userData.userid
    }
  });
  
  // Optional: Listen for events
  vapi.on('call-start', () => console.log('Interview started'));
  vapi.on('call-end', () => console.log('Interview ended'));
};