Practice Questions — Functions - Regular, Arrow, and Callback

function greet() {
  console.log("Hello!");
}

greet();
greet();

function add(a, b) {
  return a + b;
}

console.log(add(3, 7));

function multiply(a, b) {
  a * b;
}

console.log(multiply(4, 5));

const double = (n) => n * 2;

console.log(double(6));

function greet(name = "Student") {
  console.log("Hello, " + name);
}

greet("Diya");
greet();

sayHello();

function sayHello() {
  console.log("Hello!");
}

function sum(...nums) {
  let total = 0;
  for (const n of nums) {
    total += n;
  }
  return total;
}

console.log(sum(1, 2, 3, 4, 5));

const greet = function(name) {
  return "Hi, " + name;
};

console.log(greet("Arjun"));
console.log(typeof greet);

function test(a, b, c) {
  console.log(a, b, c);
}

test(1, 2);

const calc = (a, b, operation) => {
  return operation(a, b);
};

const subtract = (x, y) => x - y;

console.log(calc(10, 3, subtract));

function outer() {
  const x = 10;
  function inner() {
    console.log(x);
  }
  inner();
}

outer();

function createCounter() {
  let count = 0;
  return function() {
    count++;
    return count;
  };
}

const counter = createCounter();
console.log(counter());
console.log(counter());
console.log(counter());

(function(name) {
  console.log("Hello, " + name);
})("Priya");

const funcs = [];
for (let i = 0; i < 3; i++) {
  funcs.push(() => i);
}

console.log(funcs[0]());
console.log(funcs[1]());
console.log(funcs[2]());

function apply(arr, fn) {
  const result = [];
  for (const item of arr) {
    result.push(fn(item));
  }
  return result;
}

const nums = [1, 2, 3, 4];
console.log(apply(nums, n => n * n));

const square = n => n * n;
const cube = n => n * n * n;

function applyTo5(fn) {
  return fn(5);
}

console.log(applyTo5(square));
console.log(applyTo5(cube));

function makeGreeter(greeting) {
  return (name) => greeting + ", " + name + "!";
}

const hello = makeGreeter("Hello");
const namaste = makeGreeter("Namaste");

console.log(hello("Vikram"));
console.log(namaste("Ananya"));
console.log(hello("Kavya"));

const isEven = n => n % 2 === 0;

console.log(isEven(4));
console.log(isEven(7));

function max(a, b) {
  if (a > b) return a;
  return b;
}

console.log(max(15, 8));
console.log(max(3, 12));

const lengths = ["cat", "elephant", "dog"].map(w => w.length);
console.log(lengths);

function repeat(str, times) {
  let result = "";
  for (let i = 0; i < times; i++) {
    result += str;
  }
  return result;
}

console.log(repeat("Ha", 3));
console.log(repeat("*", 5));

const operations = {
  add: (a, b) => a + b,
  sub: (a, b) => a - b,
  mul: (a, b) => a * b
};

console.log(operations.add(5, 3));
console.log(operations.sub(10, 4));
console.log(operations.mul(6, 7));

function first(a) {
  return function second(b) {
    return a + b;
  };
}

console.log(first(10)(20));

function factorial(n) {
  if (n <= 1) return 1;
  return n * factorial(n - 1);
}

console.log(factorial(5));

const pipeline = [n => n * 2, n => n + 10, n => n / 3];

let value = 5;
for (const fn of pipeline) {
  value = fn(value);
}
console.log(value);

function compose(f, g) {
  return (x) => f(g(x));
}

const double = n => n * 2;
const addOne = n => n + 1;

const doubleThenAdd = compose(addOne, double);
console.log(doubleThenAdd(5));

console.log("Start");
setTimeout(() => console.log("Timer"), 0);
console.log("End");

const sayName = (name) => {
  console.log("Name: " + name);
};

sayName("Meera");

function once(fn) {
  let called = false;
  let result;
  return function(...args) {
    if (!called) {
      called = true;
      result = fn(...args);
    }
    return result;
  };
}

const addOnce = once((a, b) => a + b);
console.log(addOnce(3, 4));
console.log(addOnce(10, 20));
console.log(addOnce(100, 200));

const arr = [1, 2, 3];
arr.forEach((val, idx) => {
  console.log(idx + ": " + val);
});

const f = () => {};
console.log(f());

const f = (x) => x * 2;
console.log(f(f(f(3))));