Functional Programming

Question 1

What does closure mean in programming?

Answer 1

A closure is a function that remembers and can access variables from its outer (enclosing) scope, even after that outer function has finished executing.

Question 2

What is a higher-order function in functional programming?

Answer 2

A higher-order function is a function that either:
1. Takes one or more functions as arguments, or
2. Returns a function as its result.

Higher-order functions let you write more flexible, reusable, and declarative code, e.g. map(), filter(), reduce(), forEach().

Question 3

What are pure and impure functions?

Answer 3

A pure function is a function that:
1. Always returns the same output for the same input (deterministic).
2. Has no side effects — it doesn’t modify anything outside its scope (no changing external variables, no I/O operations, no mutations).

Question 4

What is idempotency, and where is it used?

Answer 4

Idempotency is a property of certain operations where performing the same operation multiple times has the same effect as performing it once, e.g. GET, PUT, DELETE are idempotent but POST is not.

Question 5

What is a monad in programming?

Answer 5

A monad is an abstraction that allows you to chain operations together while handling contextual concerns (like handling possible failure, asynchronous values, or side effects) in a clean, composable way, e.g. Promises, arrays

Question 6

How do you know if a function is composite?

Answer 6

1. If a function calls one or more functions internally and passes results from one to the other, it’s likely composite.
2. If a function is defined using composition helpers or chaining, like:
   const h = x => f(g(x));
3. Or using utility libraries (like lodash/fp or Ramda) with compose or pipe.

Question 7

When is function currying used?

Answer 7

Currying transforms a function that takes multiple arguments into a sequence of functions, each taking a single argument.

1. Partial Application: To reuse specialized versions of generic functions.
2. Functional Composition: To improve code modularity and readability.
3. Event Handling / Callbacks: To preset parameters for callbacks or event handlers in a clean way.