JavaScript Functions - Exercise 2

Question 1: What happens when an argument is omitted?

An omitted parameter receives undefined unless the function provides a default value.

javascript

function greet(name = "friend") {
  return `Hello, ${name}`;
}
console.log(greet()); // Hello, friend

Question 2: How does the rest parameter collect arguments?

A rest parameter gathers remaining arguments into a real array.

javascript

function sum(...numbers) {
  return numbers.reduce((total, number) => total + number, 0);
}
console.log(sum(2, 4, 6)); // 12

Question 3: What is a callback function?

A callback is a function passed to another function so it can be called later.

javascript

function runTask(task) {
  return task();
}
console.log(runTask(() => "Complete"));

Question 4: What makes a function higher-order?

A higher-order function accepts a function, returns a function, or does both.

javascript

function createMultiplier(factor) {
  return (value) => value * factor;
}
const double = createMultiplier(2);
console.log(double(5)); // 10

Question 5: What is the difference between a function declaration and expression?

Function declarations are hoisted with their function body; function expressions are created when execution reaches the assignment.

javascript

sayHello();
function sayHello() {
  console.log("Hello");
}
const sayBye = () => console.log("Bye");

Question 6: How can a function return multiple values?

Return an object or array, then destructure the result at the call site.

javascript

function getCoordinates() {
  return { x: 10, y: 20 };
}
const { x, y } = getCoordinates();
console.log(x, y);

Question 7: What is a pure function?

A pure function returns the same result for the same inputs and does not change outside state.

javascript

function add(left, right) {
  return left + right;
}
console.log(add(2, 3)); // 5

Question 8: Why should a function have one clear responsibility?

Small focused functions are easier to name, test, reuse, and compose into larger workflows.

javascript

function formatName(firstName, lastName) {
  return `${firstName} ${lastName}`.trim();
}
console.log(formatName("Ada", "Lovelace"));

Question 9: What is a closure?

A closure preserves access to variables from its enclosing scope after that outer function returns.

javascript

function createCounter() {
  let count = 0;
  return () => ++count;
}
const next = createCounter();
console.log(next(), next());

Question 10: How do you compose functions?

Pass the result of one focused function into the next to build a larger operation from small steps.

javascript

const trim = value => value.trim();
const upper = value => value.toUpperCase();
const format = value => upper(trim(value));
console.log(format('  hello  '));