Practice Questions — ES6+ Modern JavaScript Features

let a = 100;
let b = 200;

[a, b] = [b, a];

console.log("a =", a); // 200
console.log("b =", b); // 100

const removeDuplicates = (arr) => [...new Set(arr)];

console.log(removeDuplicates([1, 2, 2, 3, 4, 4, 5]));
// [1, 2, 3, 4, 5]

console.log(removeDuplicates(["a", "b", "a", "c", "b"]));
// ["a", "b", "c"]

const data = {
  user: {
    name: "Aarav",
    address: { city: "Delhi" },
    hobbies: ["coding", "cricket"]
  }
};

const { user: { address: { city }, hobbies: [firstHobby] } } = data;

console.log("City:", city);           // Delhi
console.log("First hobby:", firstHobby); // coding

const applySettings = (userSettings) => {
  const defaults = { theme: 'dark', fontSize: 14, language: 'en', notifications: true };
  return { ...defaults, ...userSettings };
};

console.log(applySettings({ fontSize: 18, language: 'hi' }));
// { theme: 'dark', fontSize: 18, language: 'hi', notifications: true }

console.log(applySettings({}));
// { theme: 'dark', fontSize: 14, language: 'en', notifications: true }

const safeGet = (obj, path, defaultValue = undefined) => {
  const result = path.split('.').reduce((current, key) => current?.[key], obj);
  return result ?? defaultValue;
};

const data = { user: { name: "Aarav", address: { city: "Delhi" } } };
console.log(safeGet(data, 'user.name', 'N/A'));         // "Aarav"
console.log(safeGet(data, 'user.address.city', 'N/A')); // "Delhi"
console.log(safeGet(data, 'user.phone', 'N/A'));        // "N/A"
console.log(safeGet(data, 'x.y.z', 'N/A'));             // "N/A"

const wordFrequency = (text) => {
  const map = new Map();
  const words = text.toLowerCase().split(/\s+/);
  for (const word of words) {
    if (word) {
      map.set(word, (map.get(word) || 0) + 1);
    }
  }
  return map;
};

const result = wordFrequency("the cat sat on the mat the cat");
result.forEach((count, word) => console.log(`${word}: ${count}`));
// the: 3, cat: 2, sat: 1, on: 1, mat: 1

const generateReport = ({ name, age = "unknown", ...scores }) => {
  const subjects = Object.entries(scores)
    .map(([subject, score]) => `${subject}: ${score}`)
    .join(", ");

  const values = Object.values(scores);
  const avg = Math.round(values.reduce((sum, v) => sum + v, 0) / values.length);

  return `Student: ${name} (age ${age})\nSubjects: ${subjects}\nAverage: ${avg}`;
};

console.log(generateReport({ name: "Priya", age: 15, maths: 90, science: 85, english: 92 }));
console.log();
console.log(generateReport({ name: "Aarav", maths: 78, science: 82 }));

const unique = arr => [...new Set(arr)];

const chunk = (arr, size) => {
  const result = [];
  for (let i = 0; i < arr.length; i += size) {
    result.push(arr.slice(i, i + size));
  }
  return result;
};

const zip = (a, b) => a.map((item, i) => [item, b[i]]);

const flatten = arr => arr.reduce((acc, item) => 
  [...acc, ...(Array.isArray(item) ? item : [item])], []);

console.log(unique([1, 2, 2, 3, 3]));
console.log(chunk([1, 2, 3, 4, 5], 2));
console.log(zip([1, 2, 3], ['a', 'b', 'c']));
console.log(flatten([1, [2, 3], [4, 5], 6]));