functions questions

Middleware functions in Express are functions that have access to the request, response, and the next middleware function in the application’s request-response cycle. Implement middleware by defining a function with `(req, res, next)` parameters and using `app.use(middlewareFunction)` to apply it globally or `router.use(middlewareFunction)` for specific routes. Middleware can perform tasks such as logging, authentication, or request modification.

Hooks are a feature in React 16.8+ that allow you to use state and lifecycle features in functional components. For example, `useState` lets you add state to a functional component, and `useEffect` allows you to perform side effects like fetching data. They simplify code and make it easier to reuse stateful logic.

AWS Step Functions is a service that enables you to design and orchestrate complex workflows for distributed applications. It allows you to define workflows using state machines, which represent the sequence of tasks and decisions. Step Functions coordinates the execution of AWS services such as Lambda, EC2, and SQS, managing the flow of data and handling errors and retries. It provides a visual interface for designing workflows, tracking execution progress, and debugging. This service helps simplify application development by managing the orchestration of multiple services and automating processes.

Middleware functions process requests before they reach route handlers. They can modify `req` or `res`, end the request-response cycle, or pass control. For example: `app.use((req, res, next) => { console.log('Request received'); next(); });` logs every request.

User-defined functions (UDFs) allow users to create custom functions to encapsulate reusable logic in SQL. UDFs can take parameters and return values. For example, a UDF to calculate tax could be defined as `CREATE FUNCTION CalculateTax(amount DECIMAL) RETURNS DECIMAL BEGIN RETURN amount * 0.1; END;`.

Mongoose middlewares are functions that are executed at certain stages of a document's lifecycle. For example, you can define a pre-save hook: `userSchema.pre('save', function(next) { this.age = Math.abs(this.age); next(); });`. This executes before saving, allowing you to modify data. 
 
Explain pre and post hooks.