How do you implement serverless functions with AWS Lambda in Node.js?

Question

Accepted Answer

**AWS Lambda** — serverless compute that runs code without servers.

```javascript
// handler.js
exports.handler = async (event) => {
    const { httpMethod, path, body } = event;

if (httpMethod === "GET" && path === "/users") {
        const users = await db.query("SELECT * FROM users");
        return {
            statusCode: 200,
            headers: { "Content-Type": "application/json" },
            body: JSON.stringify({ data: users }),
        };
    }

if (httpMethod === "POST" && path === "/users") {
        const data = JSON.parse(body);
        const user = await db.insert("users", data);
        return {
            statusCode: 201,
            body: JSON.stringify({ data: user }),
        };
    }

return { statusCode: 404, body: "Not found" };
};

// DB connection outside handler (reused)
const db = require("./db");
```

**Serverless Framework:**
```yaml
# serverless.yml
functions:
  api:
    handler: handler.handler
    events:
      - http:
          path: /{proxy+}
          method: ANY
```

**Key points:**
- Initialize DB connections outside handler.
- Handle cold starts.
- Use layers for shared dependencies.

Node.js: How do you implement serverless functions with AWS Lambda in Node.js?