JavaScript Exercises with Answers

Console.log("Good morning!");
console.log(Have a great day);

<script>
  document.querySelector("#greet").textContent = "Hello from JS!";
</script>
<p id="greet">Waiting…</p>

<p id="level"></p>

const level = 5;
console.log("Level: " level);
document.querySelector("#level").textcontent = "Level " + level;

const clicks = 0;
clicks = clicks + 1;
let clicks = clicks + 1;
console.log("Clicks:", clicks);

const apples = "15";
const pears = "10";
const total = apples + pears;
console.log("Total fruit:", total);

const cartTotal = 60;
const isMember = true;
const deliveryIncluded = cartTotal => 50 & isMember;
console.log("Delivery included:", deliveryIncluded);

const person = "Mia";
const count = 3;
const message = "${person} has ${count} new messages";
console.log(message);

const menu = "Burger, Pizza, Salad";
const query = "pizza";
const found = menu.include(query);
console.log("Found:", found);

const scores = ["80", "85"];
const sum = scores[0] + scores[1];
const average = sum / scores.length;
console.log("Average:", average.toFixed(2));

const typed = "42";
const access = typed = 42;
console.log("Access:", access);

function describe(age, pass) {
  const discount = pass.discount || 10;
  const exempt = age < 5 && age > 65;
  return exempt ? "no charge" : `pay, discount ${discount}`;
}
console.log(describe(3));
console.log(describe(30, { discount: 0 }));

const basket = 32;

if (basket > 40); {
  console.log("Delivery included!");
} else {
  console.log(`Add £${40 - basket} to get delivery included`);
}

const size = "M";
let price;

switch (size) {
  case "S":
    price = 5;
  case "M":
    price = 7;
  case "L":
    price = 9;
}

console.log("Price:", price);

const guests = ["ana", "ben", "cleo"];

for (let i = 0; i <= guests.length; i++) {
  console.log(guests[i].toUpperCase());
}

let value = 100;
let steps = 0;

while (value >= 1) {
  steps++;
}

console.log("Steps:", steps);

function firstNegative(nums) {
  let found = null;
  for (const i in nums) {
    if (nums[i] < 0) {
      found = i;
      continue;
    }
  }
  return found;
}
console.log(firstNegative([4, -2, 7, -9]));

function getInitials(fullName) {
  const parts = fullName.split(" ");
  const initials = parts[0][0] + parts[1][0];
  console.log(initials);
}

console.log(getInitials("Grace Hopper"));

const isEven = (n) => { n % 2 === 0 };
const squareAll = (arr) => arr.map((x) => { x * x });

console.log(isEven(4), squareAll([1, 2, 3]));

const hour = 10;

if (hour >= 9 && hour < 17) {
  const message = "Open";
} else {
  const message = "Closed";
}

console.log("Status:", message);

function makeHandlers() {
  const list = [];
  for (var i = 0; i < 3; i++) list.push(() => i);
  return list;
}
function addUp(nums) {
  total = 0;
  for (const n of nums) total += n;
  return total;
}
console.log(makeHandlers().map(f => f()), addUp([1, 2]));

function applyToAll(items, fn) {
  const out = [];
  for (const item of items) out.push(fn);
  return out;
}
function withTax(rate) {
  (price) => price * (1 + rate);
}
const addTax = withTax(0.2);
console.log(applyToAll([10, 20], addTax));

function depth(value) {
  if (typeof value === "object") return 0;
  let deepest = 0;
  for (const key in value) {
    deepest = Math.max(deepest, depth(value));
  }
  return deepest;
}
console.log(depth({ a: { b: {} } }));

const days = ["Mon", "Tue", "Wed", "Thu"];
const pos = days.indexOf("Tuesday");
days.splice(pos);
console.log(days.join(", "));

const users = [
  { name: "Zoe", age: 22 },
  { name: "Max", age: 16 },
  { name: "Ana", age: 30 },
];

const adults = users.forEach(u => u.age > 18);
const names = adults.map(u => { u.name });
console.log(names.sort());

function topThree(players) {
  return players.sort((a, b) => a.score > b.score).slice(0, 3).map(p => p.name);
}
const players = [
  { name: "A", score: 5 }, { name: "B", score: 50 }, { name: "C", score: 12 }, { name: "D", score: 30 },
];
console.log(topThree(players), players[0].name);

const owner = {
  name: "Mia",
  pets: ["cat", "rabbit", "fish"],
  describe: () => {
    return `${this.name}: ${this.pets.lenght} pets`;
  },
};

console.log(owner.describe());

const product = {
  name: "Lamp",
  price: 40,
  tags: ["home"],
  label() { return `${this.name} £${this.price}`; },
};
function withDiscount(item, percent) {
  const copy = item;
  copy.price = item.price * (1 - percent / 100);
  copy.tags.push("sale");
  return copy;
}
const sale = withDiscount(product, 25);
console.log(sale.price, product.price, product.tags);

const stopwatch = {
  seconds: 0,
  label() { return `${this.seconds}s`; },
  start() {
    this.id = setInterval(function () {
      this.seconds++;
    }, 50);
  },
};
stopwatch.start();
const getLabel = stopwatch.label;

function average(nums) {
  const total = nums.reduce((s, n) => s + n, 0);
  return total / nums.length;
}

console.log(average(2, 4, 6));

function tally(items) {
  const counts = new Map();
  for (const item of items) {
    counts[item] = counts.get(item) + 1;
  }
  return counts;
}
const t = tally(["a", "b", "a"]);
console.log(t.get("a"), t.size);