JavaScript Cheat Sheet – Complete JavaScript Syntax & Reference

const price = 120;
const quantity = 3;
const discount = 20;

const subtotal = price * quantity;
const total = subtotal - discount;
const averagePrice = total / quantity;

console.log(subtotal);
console.log(total);
console.log(averagePrice);

const number = 17;

const isEven = number % 2 === 0;
const isOdd = number % 2 !== 0;

console.log(isEven);
console.log(isOdd);
console.log(17 % 5);

const colors = ["red", "green", "blue"];

for (let index = 0; index < 7; index++) {
  const color = colors[index % colors.length];
  console.log(color);
}

const square = 5 ** 2;
const cube = 4 ** 3;
const squareRoot = 81 ** 0.5;

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

let firstValue = 5;
let secondValue = 5;

const postfixResult = firstValue++;
const prefixResult = ++secondValue;

console.log(postfixResult);
console.log(firstValue);

console.log(prefixResult);
console.log(secondValue);

// Less readable
const result = counter++ + ++counter;

// Clearer
counter += 1;
const firstValue = counter;

counter += 1;
const secondValue = counter;

const result = firstValue + secondValue;

const numericString = "42";
const decimalString = "19.95";
const invalidNumber = "JavaScript";

console.log(+numericString);
console.log(+decimalString);
console.log(+invalidNumber);
console.log(-numericString);

console.log(10 + 5);
console.log("10" + 5);
console.log(10 + "5");
console.log(10 + 5 + "px");
console.log("Total: " + 10 + 5);

const firstInput = "25";
const secondInput = "15";

// Incorrect for numeric addition
const concatenatedResult = firstInput + secondInput;

// Correct
const numericResult = Number(firstInput) + Number(secondInput);

console.log(concatenatedResult);
console.log(numericResult);

console.log(10 / 0);
console.log(-10 / 0);
console.log(0 / 0);
console.log("hello" * 5);

function divideNumbers(dividend, divisor) {
  const result = dividend / divisor;

  if (!Number.isFinite(result)) {
    return "The calculation did not produce a finite number.";
  }

  return result;
}

console.log(divideNumbers(20, 4));
console.log(divideNumbers(20, 0));

const result = 0.1 + 0.2;

console.log(result);
console.log(result === 0.3);

const firstPriceInCents = 10;
const secondPriceInCents = 20;

const totalInCents = firstPriceInCents + secondPriceInCents;
const totalInDollars = totalInCents / 100;

console.log(totalInDollars);

let score = 100;

score = 250;

console.log(score);

let total = 20;

total += 5;
total *= 2;
total -= 10;
total /= 3;

console.log(total);

let value = "10";

value += 5;

console.log(value);

let username = "";

username ||= "Guest";

console.log(username);

let isLoggedIn = true;

isLoggedIn &&= false;

console.log(isLoggedIn);

let theme = null;
let age = 0;

theme ??= "Light";
age ??= 18;

console.log(theme);
console.log(age);

const age = 20;

if (age >= 18) {
    console.log("Access granted");
} else {
    console.log("Access denied");
}

const score = 92;

const passed = score >= 50;
const perfect = score === 100;

console.log(passed);
console.log(perfect);

console.log(5 == "5");
console.log(false == 0);
console.log(null == undefined);

console.log(5 === "5");
console.log(false === 0);
console.log(null === undefined);
console.log(5 === 5);

const userAge = "18";

if (Number(userAge) === 18) {
    console.log("Adult");
}

const temperature = 24;

console.log(temperature > 20);
console.log(temperature < 0);
console.log(temperature >= 24);
console.log(temperature <= 30);

const score = 78;

if (score >= 50) {
    console.log("You passed the exam.");
} else {
    console.log("You failed the exam.");
}

const age = 25;
const hasTicket = true;

const canEnter = age >= 18 && hasTicket;

console.log(canEnter);

const isAdmin = false;
const isModerator = true;

const hasAccess = isAdmin || isModerator;

console.log(hasAccess);

const isLoggedIn = false;

console.log(!isLoggedIn);

const isLoggedIn = false;

isLoggedIn && console.log("Welcome!");

const username = "";

const displayName = username || "Guest";

console.log(displayName);

console.log(Boolean([]));
console.log(Boolean({}));
console.log(Boolean("Hello"));
console.log(Boolean(42));

console.log(Boolean(""));
console.log(Boolean(0));
console.log(Boolean(null));

const age = 20;

const access =
    age >= 18 ? "Allowed" : "Denied";

console.log(access);

// Ternary
const status = score >= 50
    ? "Pass"
    : "Fail";

// if...else
let result;

if (score >= 50) {
    result = "Pass";
} else {
    result = "Fail";
}

// Avoid
const grade =
    score >= 90 ? "A" :
    score >= 80 ? "B" :
    score >= 70 ? "C" :
    "F";

const username = null;

const displayName = username ?? "Guest";

console.log(displayName);

const quantity = 0;

console.log(quantity || 10);
console.log(quantity ?? 10);

const user = null;

// Throws an error
console.log(user.name);

const user = null;

console.log(user?.name);

const customer = {
    profile: {
        address: {
            city: "London"
        }
    }
};

console.log(customer?.profile?.address?.city);
console.log(customer?.profile?.phone?.mobile);

const user = {};

user.sayHello?.();

console.log(typeof 42);
console.log(typeof "Hello");
console.log(typeof true);
console.log(typeof undefined);
console.log(typeof {});

console.log(typeof null);

const today = new Date();
const items = [];

console.log(today instanceof Date);
console.log(items instanceof Array);
console.log(items instanceof Object);

const user = {
    name: "Maya",
    email: undefined
};

console.log("name" in user);
console.log("email" in user);
console.log("age" in user);

const settings = {
    theme: undefined
};

console.log("theme" in settings);
console.log(settings.theme !== undefined);

const user = {
    name: "Maya"
};

console.log("toString" in user);
console.log(Object.hasOwn(user, "toString"));
console.log(Object.hasOwn(user, "name"));

console.log(5 & 3);
console.log(5 | 3);
console.log(5 ^ 3);

console.log(8 << 1);
console.log(8 >> 1);

const result = 10 + 5 * 2;

console.log(result);

10 + (5 * 2)

const result = (10 + 5) * 2;

console.log(result);

if (userAge === 18) {
    console.log("Adult");
}

// Good
const total = (price + tax) * quantity;

// Harder to read
const total = price + tax * quantity;

const quantity = 0;

const value = quantity ?? 1;

const isAdult = age >= 18;
const hasPermission = user.role === "admin";

if (isAdult && hasPermission) {
    // ...
}

console.log(5 == "5");

const quantity = 0;

console.log(quantity || 10);

const total = 10 + 5 * 2;

console.log(total);

console.log(Boolean([]));
console.log(Boolean({}));

// Hard to read
const grade =
score >= 90 ? "A" :
score >= 80 ? "B" :
score >= 70 ? "C" :
"F";

console.log(typeof null);

const first = "JavaScript";
const second = 'Cheat Sheet';
const third = `Learn ${first}`;

console.log(first);
console.log(second);
console.log(third);

let language = "JavaScript";

language[0] = "X";

console.log(language);

language = "TypeScript";

console.log(language);

const language = "JavaScript";

console.log(language.length);

const word = "JavaScript";

console.log(word[0]);
console.log(word.charAt(4));
console.log(word.at(-1));

const name = "Alice";
const lessons = 12;

const message =
  `${name} completed ${lessons} lessons.`;

console.log(message);

const message = `JavaScript
Strings
Cheat Sheet`;

console.log(message);

const firstName = "Alice";
const lastName = "Johnson";

const fullName =
  firstName + " " + lastName;

const modernName =
  `${firstName} ${lastName}`;

console.log(fullName);
console.log(modernName);

const text = "JavaScript";

console.log(text.toUpperCase());
console.log(text.toLowerCase());
console.log(text);

const input = "   Alice   ";

console.log(input);
console.log(input.trim());

const text =
  "Learn JavaScript today";

console.log(
  text.includes("JavaScript")
);

console.log(
  text.startsWith("Learn")
);

console.log(
  text.endsWith("today")
);

console.log(
  text.indexOf("JavaScript")
);

const language = "JavaScript";

console.log(
  language.slice(0, 4)
);

console.log(
  language.slice(4)
);

console.log(
  language.slice(-6)
);

const sentence =
  "JavaScript is fun. JavaScript is useful.";

console.log(
  sentence.replace(
    "JavaScript",
    "TypeScript"
  )
);

console.log(
  sentence.replaceAll(
    "JavaScript",
    "TypeScript"
  )
);

console.log(
  "-".repeat(10)
);

console.log(
  "7".padStart(3, "0")
);

console.log(
  "JS".padEnd(5, ".")
);

const languages =
  "JavaScript,Python,SQL";

const result =
  languages.split(",");

console.log(result);

const title =
  "javascript string methods";

const formatted = title
  .split(" ")
  .map(word =>
    word[0].toUpperCase() +
    word.slice(1)
  )
  .join(" ");

console.log(formatted);

const text =
  "Order 12 contains 3 products";

const numbers =
  text.match(/\d+/g);

console.log(numbers);

const text =
  "JavaScript 2025, Python 2026";

const matches =
  text.matchAll(
    /([A-Za-z]+) (\d{4})/g
  );

for (const match of matches) {
  console.log(
    match[1],
    match[2],
    match.index
  );
}

const text =
  "Learn JavaScript";

console.log(
  /javascript/i.test(text)
);

console.log(
  text.search(/javascript/i)
);

const phone =
  "555 123 4567";

const formatted =
  phone.replace(
    /\s+/g,
    "-"
  );

console.log(formatted);

const text =
  "Products: 5, price: 20";

const result =
  text.replace(
    /\d+/g,
    match =>
      String(Number(match) * 2)
  );

console.log(result);

console.log(
  "JavaScript" === "JavaScript"
);

console.log(
  "JavaScript" === "javascript"
);

console.log(
  "Hello" === "Hello "
);

const first =
  " JavaScript ";

const second =
  "javascript";

const isEqual =
  first.trim().toLowerCase() ===
  second.trim().toLowerCase();

console.log(isEqual);

const names = [
  "Östen",
  "Anna",
  "Åke",
  "Älva"
];

names.sort((first, second) =>
  first.localeCompare(
    second,
    "sv"
  )
);

console.log(names);

const number = 42;
const active = true;
const missing = null;

console.log(
  String(number)
);

console.log(
  String(active)
);

console.log(
  String(missing)
);

const message =
  "First line\nSecond line";

const quote =
  "She said, \"Hello!\"";

const path =
  "C:\\Users\\Alice";

console.log(message);
console.log(quote);
console.log(path);

const path =
  String.raw`C:\Users\Alice`;

console.log(path);

const emoji = "😊";

console.log(
  emoji.length
);

console.log(
  [...emoji].length
);

const text = "A😊B";

for (const character of text) {
  console.log(character);
}

const emoji = "😊";

const codePoint =
  emoji.codePointAt(0);

console.log(codePoint);

console.log(
  String.fromCodePoint(codePoint)
);

const first = "\u00E9";
const second = "e\u0301";

console.log(
  first === second
);

console.log(
  first.normalize() ===
  second.normalize()
);

function highlight(
  strings,
  ...values
) {
  return strings.reduce(
    (result, text, index) =>
      result +
      text +
      (
        index < values.length
          ? `[${values[index]}]`
          : ""
      ),
    ""
  );
}

const language = "JavaScript";
const level = "Beginner";

const result =
  highlight`${language} level: ${level}`;

console.log(result);

const primitive =
  "JavaScript";

const object =
  new String("JavaScript");

console.log(
  typeof primitive
);

console.log(
  typeof object
);

console.log(
  primitive === object
);

function createSlug(title) {
  return title
    .trim()
    .toLowerCase()
    .replace(
      /[^a-z0-9]+/g,
      "-"
    )
    .replace(
      /^-|-$/g,
      ""
    );
}

console.log(
  createSlug(
    " JavaScript String Methods! "
  )
);

function maskCard(number) {
  const text =
    String(number);

  return text
    .slice(-4)
    .padStart(
      text.length,
      "*"
    );
}

console.log(
  maskCard("1234567812345678")
);

function countWords(text) {
  const cleaned =
    text.trim();

  if (!cleaned) {
    return 0;
  }

  return cleaned
    .split(/\s+/)
    .length;
}

console.log(
  countWords(
    "Learn modern JavaScript today"
  )
);

function truncate(
  text,
  maximumLength
) {
  if (
    text.length <=
    maximumLength
  ) {
    return text;
  }

  return (
    text.slice(
      0,
      maximumLength - 3
    ) + "..."
  );
}

console.log(
  truncate(
    "JavaScript string methods",
    18
  )
);

const languages = [
  "JavaScript",
  "Python",
  "SQL"
];

console.log(languages);

const mixedValues = [
  "JavaScript",
  42,
  true,
  null,
  { level: "Beginner" },
  ["HTML", "CSS"]
];

console.log(mixedValues);

const languages = [
  "JavaScript",
  "Python",
  "SQL"
];

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

const colors = [
  "red",
  "green",
  "blue"
];

console.log(colors[10]);

const languages = [
  "JavaScript",
  "Python",
  "SQL"
];

console.log(
  languages.length
);

const languages = [
  "JavaScript",
  "Python",
  "SQL"
];

console.log(
  languages[
    languages.length - 1
  ]
);

console.log(
  languages.at(-1)
);

const languages = [
  "JavaScript",
  "Python",
  "SQL"
];

languages[1] =
  "TypeScript";

console.log(languages);

const colors = [
  "red",
  "green"
];

colors[0] = "blue";

console.log(colors);

const languages = [
  "JavaScript",
  "Python"
];

languages[
  languages.length
] = "SQL";

console.log(languages);

const values = [
  "A",
  "B"
];

values[5] = "F";

console.log(values);
console.log(values.length);

const languages = [
  "JavaScript",
  "Python"
];

console.log(
  Array.isArray(languages)
);

console.log(
  typeof languages
);

const characters =
  Array.from("JavaScript");

console.log(characters);

const numbers =
  Array.from(
    { length: 5 },
    (_, index) =>
      index + 1
  );

console.log(numbers);

const original = [
  "JavaScript",
  "Python"
];

const spreadCopy = [
  ...original
];

const sliceCopy =
  original.slice();

spreadCopy.push("SQL");

console.log(original);
console.log(spreadCopy);
console.log(sliceCopy);

const original = [
  {
    name: "Alice"
  }
];

const copy = [
  ...original
];

copy[0].name = "Maya";

console.log(
  original[0].name
);

console.log(
  copy[0].name
);

const frontend = [
  "HTML",
  "CSS"
];

const programming = [
  "JavaScript",
  "Python"
];

const skills = [
  ...frontend,
  ...programming
];

console.log(skills);

const grid = [
  ["A1", "A2"],
  ["B1", "B2"],
  ["C1", "C2"]
];

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

const users = [
  {
    id: 1,
    name: "Alice",
    active: true
  },
  {
    id: 2,
    name: "Bob",
    active: false
  }
];

console.log(
  users[0].name
);

console.log(
  users[1].active
);

const languages = [
  "JavaScript",
  "Python"
];

const newLength =
  languages.push(
    "SQL",
    "PHP"
  );

console.log(languages);
console.log(newLength);

const languages = [
  "JavaScript",
  "Python",
  "SQL"
];

const removed =
  languages.pop();

console.log(removed);
console.log(languages);

const queue = [
  "Second",
  "Third"
];

const newLength =
  queue.unshift("First");

console.log(queue);
console.log(newLength);

const queue = [
  "First",
  "Second",
  "Third"
];

const removed =
  queue.shift();

console.log(removed);
console.log(queue);

const colors = [
  "red",
  "green",
  "blue",
  "yellow"
];

const removed =
  colors.splice(1, 2);

console.log(colors);
console.log(removed);

const languages = [
  "JavaScript",
  "SQL"
];

languages.splice(
  1,
  0,
  "Python",
  "TypeScript"
);

console.log(languages);

const languages = [
  "JavaScript",
  "Python",
  "SQL"
];

const removed =
  languages.splice(
    1,
    1,
    "TypeScript"
  );

console.log(languages);
console.log(removed);

const values = [
  "A",
  "B",
  "C",
  "D"
];

values.splice(
  -2,
  1,
  "X"
);

console.log(values);

const languages = [
  "JavaScript",
  "Python",
  "SQL"
];

const updated =
  languages.toSpliced(
    1,
    1,
    "TypeScript"
  );

console.log(languages);
console.log(updated);

const numbers = [
  1,
  2,
  3,
  4
];

const reversed =
  numbers.reverse();

console.log(numbers);
console.log(reversed);
console.log(
  numbers === reversed
);

const numbers = [
  1,
  2,
  3,
  4
];

const reversed =
  numbers.toReversed();

console.log(numbers);
console.log(reversed);

const values = [
  1,
  2,
  3,
  4,
  5
];

values.fill(
  0,
  1,
  4
);

console.log(values);

const users =
  new Array(3).fill({
    active: false
  });

users[0].active = true;

console.log(users);

const values = [
  "A",
  "B",
  "C",
  "D",
  "E"
];

values.copyWithin(
  0,
  3
);

console.log(values);

const values = [
  1,
  2,
  3,
  4,
  5
];

values.copyWithin(
  1,
  3,
  5
);

console.log(values);

const values = [
  "A",
  "B",
  "C",
  "D"
];

values.length = 2;

console.log(values);

const values = [
  "A",
  "B"
];

values.length = 5;

console.log(values);
console.log(values.length);

const firstReference = [
  1,
  2,
  3
];

const secondReference =
  firstReference;

firstReference.length = 0;

console.log(firstReference);
console.log(secondReference);

const original = [
  "JavaScript",
  "Python"
];

const shared =
  original;

shared.push("SQL");

console.log(original);
console.log(shared);

const languages = [
  "JavaScript",
  "Python",
  "SQL"
];

const updated =
  languages.with(
    1,
    "TypeScript"
  );

console.log(languages);
console.log(updated);

const languages = [
  "JavaScript",
  "Python",
  "SQL"
];

languages.forEach(
  (language, index, array) => {
    console.log(
      language,
      index,
      array.length
    );
  }
);

const prices = [
  10,
  20,
  30
];

prices.forEach(price => {
  console.log(
    `$${price}`
  );
});

const numbers = [
  1,
  2,
  3,
  4
];

const doubled =
  numbers.map(number =>
    number * 2
  );

console.log(numbers);
console.log(doubled);

const users = [
  {
    id: 1,
    name: "Alice"
  },
  {
    id: 2,
    name: "Bob"
  }
];

const names =
  users.map(user =>
    user.name
  );

console.log(names);

const names = [
  "Alice",
  "Bob"
];

const users =
  names.map(
    (name, index) => ({
      id: index + 1,
      name
    })
  );

console.log(users);

const numbers = [
  1,
  2,
  3,
  4,
  5,
  6
];

const evenNumbers =
  numbers.filter(number =>
    number % 2 === 0
  );

console.log(evenNumbers);

const users = [
  {
    name: "Alice",
    active: true
  },
  {
    name: "Bob",
    active: false
  },
  {
    name: "Maya",
    active: true
  }
];

const activeUsers =
  users.filter(user =>
    user.active
  );

console.log(activeUsers);

const values = [
  "JavaScript",
  "",
  null,
  "Python",
  undefined,
  0,
  "SQL"
];

const cleaned =
  values.filter(Boolean);

console.log(cleaned);

const users = [
  {
    id: 1,
    name: "Alice"
  },
  {
    id: 2,
    name: "Bob"
  }
];

const user =
  users.find(item =>
    item.id === 2
  );

console.log(user);

const users = [
  {
    id: 1,
    name: "Alice"
  },
  {
    id: 2,
    name: "Bob"
  }
];

const index =
  users.findIndex(user =>
    user.id === 2
  );

console.log(index);

const numbers = [
  3,
  8,
  4,
  10,
  6
];

console.log(
  numbers.findLast(
    number =>
      number > 5
  )
);

console.log(
  numbers.findLastIndex(
    number =>
      number > 5
  )
);

const scores = [
  42,
  58,
  91,
  67
];

const hasHighScore =
  scores.some(score =>
    score >= 90
  );

console.log(hasHighScore);

const ages = [
  24,
  31,
  19,
  42
];

const allAdults =
  ages.every(age =>
    age >= 18
  );

console.log(allAdults);

const prices = [
  10,
  20,
  30
];

const total =
  prices.reduce(
    (sum, price) =>
      sum + price,
    0
  );

console.log(total);

const values = [];

const total =
  values.reduce(
    (sum, value) =>
      sum + value,
    0
  );

console.log(total);

const colors = [
  "red",
  "blue",
  "red",
  "green",
  "blue",
  "red"
];

const counts =
  colors.reduce(
    (result, color) => {
      result[color] =
        (result[color] ?? 0) + 1;

      return result;
    },
    {}
  );

console.log(counts);

const products = [
  {
    name: "Laptop",
    category: "Tech"
  },
  {
    name: "Mouse",
    category: "Tech"
  },
  {
    name: "Chair",
    category: "Furniture"
  }
];

const grouped =
  products.reduce(
    (result, product) => {
      const category =
        product.category;

      result[category] ??= [];

      result[category].push(
        product
      );

      return result;
    },
    {}
  );

console.log(grouped);

const words = [
  "JavaScript",
  "is",
  "powerful"
];

const result =
  words.reduceRight(
    (sentence, word) =>
      sentence
        ? `${sentence} ${word}`
        : word,
    ""
  );

console.log(result);

const values = [
  1,
  [2, 3],
  [4, [5, 6]]
];

console.log(
  values.flat()
);

console.log(
  values.flat(2)
);

const deeplyNested = [
  1,
  [2, [3, [4]]]
];

const flatValues =
  deeplyNested.flat(
    Infinity
  );

console.log(flatValues);

const sentences = [
  "Learn JavaScript",
  "Build projects"
];

const words =
  sentences.flatMap(
    sentence =>
      sentence.split(" ")
  );

console.log(words);

const numbers = [
  1,
  2,
  3,
  4
];

const result =
  numbers.flatMap(
    number =>
      number % 2 === 0
        ? [
            number,
            number * 10
          ]
        : []
  );

console.log(result);

const products = [
  {
    name: "Laptop",
    price: 1200,
    active: true
  },
  {
    name: "Mouse",
    price: 40,
    active: false
  },
  {
    name: "Keyboard",
    price: 80,
    active: true
  }
];

const total =
  products
    .filter(product =>
      product.active
    )
    .map(product =>
      product.price
    )
    .reduce(
      (sum, price) =>
        sum + price,
      0
    );

console.log(total);

const languages = [
  "JavaScript",
  "Python",
  "SQL"
];

console.log(
  languages.includes(
    "Python"
  )
);

console.log(
  languages.includes(
    "PHP"
  )
);

const colors = [
  "red",
  "green",
  "blue",
  "green"
];

console.log(
  colors.indexOf(
    "green"
  )
);

console.log(
  colors.indexOf(
    "yellow"
  )
);

const colors = [
  "red",
  "green",
  "blue",
  "green"
];

console.log(
  colors.lastIndexOf(
    "green"
  )
);

const values = [
  10,
  NaN,
  20
];

console.log(
  values.includes(NaN)
);

console.log(
  values.indexOf(NaN)
);

const languages = [
  "Python",
  "JavaScript",
  "CSS",
  "HTML"
];

languages.sort();

console.log(languages);

const numbers = [
  2,
  100,
  15,
  8
];

numbers.sort();

console.log(numbers);

const numbers = [
  2,
  100,
  15,
  8
];

numbers.sort(
  (first, second) =>
    first - second
);

console.log(numbers);

const numbers = [
  2,
  100,
  15,
  8
];

numbers.sort(
  (first, second) =>
    second - first
);

console.log(numbers);

const products = [
  {
    name: "Keyboard",
    price: 80
  },
  {
    name: "Laptop",
    price: 1200
  },
  {
    name: "Mouse",
    price: 40
  }
];

products.sort(
  (first, second) =>
    first.price -
    second.price
);

console.log(products);

const users = [
  {
    name: "Maya"
  },
  {
    name: "Alice"
  },
  {
    name: "Bob"
  }
];

users.sort(
  (first, second) =>
    first.name.localeCompare(
      second.name
    )
);

console.log(users);

const numbers = [
  20,
  5,
  100,
  12
];

const sorted =
  numbers.toSorted(
    (first, second) =>
      first - second
  );

console.log(numbers);
console.log(sorted);

const numbers = [
  20,
  5,
  100,
  12
];

const sorted = [
  ...numbers
].sort(
  (first, second) =>
    first - second
);

console.log(numbers);
console.log(sorted);

const users = [
  {
    name: "Maya",
    age: 30
  },
  {
    name: "Alice",
    age: 25
  },
  {
    name: "Bob",
    age: 25
  }
];

const sorted =
  users.toSorted(
    (first, second) =>
      first.age -
        second.age ||
      first.name.localeCompare(
        second.name
      )
  );

console.log(sorted);

const languages = [
  "JavaScript",
  "Python",
  "SQL"
];

const [
  first,
  second,
  third
] = languages;

console.log(first);
console.log(second);
console.log(third);

const values = [
  "A",
  "B",
  "C"
];

const [
  first,
  ,
  third
] = values;

console.log(first);
console.log(third);

const values = [
  "JavaScript"
];

const [
  language,
  level = "Beginner"
] = values;

console.log(language);
console.log(level);

const values = [
  10,
  20,
  30,
  40
];

const [
  first,
  ...remaining
] = values;

console.log(first);
console.log(remaining);

let first = "A";
let second = "B";

[
  first,
  second
] = [
  second,
  first
];

console.log(first);
console.log(second);

const matrix = [
  [1, 2, 3],
  [4, 5, 6],
  [7, 8, 9]
];

console.log(
  matrix[1][2]
);

const matrix = [
  [1, 2],
  [3, 4],
  [5, 6]
];

for (const row of matrix) {
  for (const value of row) {
    console.log(value);
  }
}

const values = [
  "JavaScript",
  "Python",
  "JavaScript",
  "SQL",
  "Python"
];

const uniqueValues = [
  ...new Set(values)
];

console.log(uniqueValues);

const users = [
  {
    id: 1,
    name: "Alice"
  },
  {
    id: 2,
    name: "Bob"
  },
  {
    id: 1,
    name: "Alice"
  }
];

const uniqueUsers = [
  ...new Map(
    users.map(user => [
      user.id,
      user
    ])
  ).values()
];

console.log(uniqueUsers);

const users = [
  {
    id: 1,
    name: "Alice"
  },
  {
    id: 2,
    name: "Bob"
  }
];

const usersById =
  new Map(
    users.map(user => [
      user.id,
      user
    ])
  );

console.log(
  usersById.get(2)
);

const numbers = [
  12,
  5,
  87,
  24
];

console.log(
  Math.min(...numbers)
);

console.log(
  Math.max(...numbers)
);

const scores = [
  80,
  90,
  70,
  100
];

const total =
  scores.reduce(
    (sum, score) =>
      sum + score,
    0
  );

const average =
  scores.length
    ? total / scores.length
    : 0;

console.log(average);

function shuffle(values) {
  const result = [
    ...values
  ];

  for (
    let index =
      result.length - 1;
    index > 0;
    index--
  ) {
    const randomIndex =
      Math.floor(
        Math.random() *
        (index + 1)
      );

    [
      result[index],
      result[randomIndex]
    ] = [
      result[randomIndex],
      result[index]
    ];
  }

  return result;
}

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

const first = [
  1,
  2,
  3
];

const second = [
  1,
  2,
  3
];

const shared = first;

console.log(
  first === second
);

console.log(
  first === shared
);

function arraysEqual(
  first,
  second
) {
  return (
    first.length ===
      second.length &&
    first.every(
      (value, index) =>
        Object.is(
          value,
          second[index]
        )
    )
  );
}

console.log(
  arraysEqual(
    [1, 2, 3],
    [1, 2, 3]
  )
);

console.log(
  arraysEqual(
    [1, 2, 3],
    [3, 2, 1]
  )
);

const user = {
  name: "Alice",
  age: 30,
  active: true
};

console.log(user);

const user = {
  name: "Alice",
  age: 30
};

console.log(user.name);
console.log(user.age);

const user = {
  name: "Alice",
  "account status": "active"
};

console.log(
  user["name"]
);

console.log(
  user["account status"]
);

const user = {
  name: "Alice",
  age: 30
};

const propertyName =
  "name";

console.log(
  user[propertyName]
);

const user = {
  name: "Alice"
};

user.age = 30;

user["account status"] =
  "active";

console.log(user);

const user = {
  name: "Alice",
  age: 30
};

user.name = "Maya";
user.age = 31;

console.log(user);

const user = {
  name: "Alice",
  age: 30,
  password: "secret"
};

const deleted =
  delete user.password;

console.log(deleted);
console.log(user);

const user = {
  name: "Alice"
};

console.log(
  user.email
);

const user = {
  name: "Alice",
  email: undefined
};

console.log(
  Object.hasOwn(
    user,
    "name"
  )
);

console.log(
  Object.hasOwn(
    user,
    "email"
  )
);

console.log(
  Object.hasOwn(
    user,
    "age"
  )
);

const user = {
  name: "Alice"
};

console.log(
  "name" in user
);

console.log(
  "toString" in user
);

console.log(
  "email" in user
);

const fieldName =
  "email";

const user = {
  name: "Alice",
  [fieldName]:
    "alice@example.com"
};

console.log(user);

const name = "Alice";
const age = 30;
const active = true;

const user = {
  name,
  age,
  active
};

console.log(user);

const user = {
  name: "Alice",

  greet: function () {
    return "Hello!";
  }
};

console.log(
  user.greet()
);

const user = {
  name: "Alice",

  greet() {
    return `Hello ${this.name}`;
  }
};

console.log(
  user.greet()
);

const product = {
  name: "Keyboard",
  price: 80,
  quantity: 2,

  getTotal() {
    return (
      this.price *
      this.quantity
    );
  }
};

console.log(
  product.getTotal()
);

const user = {
  name: "Alice",

  address: {
    city: "London",
    country: "UK"
  }
};

console.log(
  user.address.city
);

console.log(
  user["address"]["country"]
);

const course = {
  title:
    "JavaScript Fundamentals",

  topics: [
    "Variables",
    "Arrays",
    "Objects"
  ]
};

console.log(
  course.topics[1]
);

const user = {
  name: "Alice"
};

console.log(
  user.address?.city
);

console.log(
  user.profile?.settings?.theme
);

const user = {
  name: "Alice"
};

const result =
  user.greet?.();

console.log(result);

const user = {
  name: "Alice",
  settings: {
    theme: null
  }
};

const theme =
  user.settings?.theme ??
  "system";

console.log(theme);

const user = {
  name: "Alice"
};

user.name = "Maya";
user.active = true;

console.log(user);

const firstUser = {
  name: "Alice"
};

const secondUser =
  firstUser;

secondUser.name = "Maya";

console.log(
  firstUser.name
);

console.log(
  secondUser.name
);

const first = {
  name: "Alice"
};

const second = {
  name: "Alice"
};

const shared = first;

console.log(
  first === second
);

console.log(
  first === shared
);

const user = {
  name: "Alice",
  age: 30,
  active: true
};

const keys =
  Object.keys(user);

console.log(keys);

const settings = {
  theme: "dark",
  language: "en",
  notifications: true
};

const propertyCount =
  Object.keys(settings).length;

console.log(propertyCount);

const user = {
  name: "Alice",
  age: 30,
  active: true
};

for (
  const key of
  Object.keys(user)
) {
  console.log(
    key,
    user[key]
  );
}

const product = {
  name: "Laptop",
  price: 1200,
  stock: 5,
  active: true
};

const numericKeys =
  Object.keys(product)
    .filter(key =>
      typeof product[key] ===
      "number"
    );

console.log(numericKeys);

const user = {
  name: "Alice",
  age: 30,
  active: true
};

const values =
  Object.values(user);

console.log(values);

const monthlySales = {
  january: 1200,
  february: 1500,
  march: 1800
};

const total =
  Object.values(
    monthlySales
  ).reduce(
    (sum, value) =>
      sum + value,
    0
  );

console.log(total);

const permissions = {
  read: true,
  write: false,
  delete: false
};

const hasPermission =
  Object.values(
    permissions
  ).some(Boolean);

const hasAllPermissions =
  Object.values(
    permissions
  ).every(Boolean);

console.log(hasPermission);
console.log(
  hasAllPermissions
);

const user = {
  name: "Alice",
  age: 30,
  active: true
};

const entries =
  Object.entries(user);

console.log(entries);

const product = {
  name: "Keyboard",
  price: 80,
  stock: 12
};

for (
  const [key, value] of
  Object.entries(product)
) {
  console.log(
    `${key}: ${value}`
  );
}

const user = {
  name: "Alice",
  age: 30,
  password: "secret",
  active: true
};

const publicUser =
  Object.fromEntries(
    Object.entries(user)
      .filter(
        ([key]) =>
          key !== "password"
      )
  );

console.log(publicUser);

const prices = {
  laptop: 1200,
  keyboard: 80,
  mouse: 40
};

const discountedPrices =
  Object.fromEntries(
    Object.entries(prices)
      .map(
        ([key, value]) => [
          key,
          value * 0.9
        ]
      )
  );

console.log(
  discountedPrices
);

const settings = {
  darkMode: true,
  emailAlerts: false
};

const uppercaseKeys =
  Object.fromEntries(
    Object.entries(settings)
      .map(
        ([key, value]) => [
          key.toUpperCase(),
          value
        ]
      )
  );

console.log(
  uppercaseKeys
);

const entries = [
  ["name", "Alice"],
  ["age", 30],
  ["active", true]
];

const user =
  Object.fromEntries(
    entries
  );

console.log(user);

const settingsMap =
  new Map([
    ["theme", "dark"],
    ["language", "en"],
    ["notifications", true]
  ]);

const settings =
  Object.fromEntries(
    settingsMap
  );

console.log(settings);

const parameters =
  new URLSearchParams(
    "page=2&sort=price&order=asc"
  );

const query =
  Object.fromEntries(
    parameters
  );

console.log(query);

const user = {
  name: "Alice",
  email: undefined
};

console.log(
  Object.hasOwn(
    user,
    "name"
  )
);

console.log(
  Object.hasOwn(
    user,
    "email"
  )
);

console.log(
  Object.hasOwn(
    user,
    "toString"
  )
);

const user = {
  name: "Alice"
};

console.log(
  Object.hasOwn(
    user,
    "toString"
  )
);

console.log(
  "toString" in user
);

const data =
  Object.create(null);

data.name = "Alice";

console.log(
  Object.hasOwn(
    data,
    "name"
  )
);

const user = {
  name: "Alice"
};

Object.defineProperty(
  user,
  "id",
  {
    value: 123,
    enumerable: false
  }
);

console.log(
  Object.keys(user)
);

console.log(user.id);

const identifier =
  Symbol("id");

const user = {
  name: "Alice",
  [identifier]: 123
};

console.log(
  Object.keys(user)
);

console.log(
  user[identifier]
);

const user = {
  name: "Alice"
};

Object.defineProperty(
  user,
  "id",
  {
    value: 123,
    enumerable: false
  }
);

console.log(
  Object.getOwnPropertyNames(
    user
  )
);

const identifier =
  Symbol("id");

const user = {
  name: "Alice",
  [identifier]: 123
};

const symbols =
  Object.getOwnPropertySymbols(
    user
  );

console.log(symbols);
console.log(
  user[symbols[0]]
);

const identifier =
  Symbol("id");

const user = {
  name: "Alice",
  [identifier]: 123
};

Object.defineProperty(
  user,
  "secret",
  {
    value: true,
    enumerable: false
  }
);

console.log(
  Reflect.ownKeys(user)
);

const original = {
  name: "Alice",
  age: 30
};

const copy = {
  ...original
};

copy.name = "Maya";

console.log(original);
console.log(copy);

const original = {
  name: "Alice",
  age: 30
};

const copy =
  Object.assign(
    {},
    original
  );

copy.age = 31;

console.log(original);
console.log(copy);

const user = {
  id: 1,
  name: "Alice",
  active: false
};

const updatedUser = {
  ...user,
  active: true
};

console.log(user);
console.log(updatedUser);

const user = {
  name: "Alice",
  age: 30
};

const updatedUser = {
  ...user,
  role: "admin"
};

console.log(updatedUser);

const user = {
  name: "Alice",
  age: 30,
  password: "secret"
};

const {
  password,
  ...publicUser
} = user;

console.log(publicUser);
console.log(password);

const user = {
  name: "Alice",
  age: 30,
  password: "secret"
};

const keyToRemove =
  "password";

const {
  [keyToRemove]: removed,
  ...remaining
} = user;

console.log(remaining);
console.log(removed);

const defaults = {
  theme: "light",
  language: "en",
  notifications: true
};

const preferences = {
  theme: "dark",
  notifications: false
};

const settings = {
  ...defaults,
  ...preferences
};

console.log(settings);

const defaults = {
  theme: "light",
  language: "en"
};

const preferences = {
  theme: "dark"
};

const settings =
  Object.assign(
    {},
    defaults,
    preferences
  );

console.log(settings);

const settings = {
  theme: "light"
};

const result =
  Object.assign(
    settings,
    {
      theme: "dark",
      language: "en"
    }
  );

console.log(settings);
console.log(
  settings === result
);

const original = {
  name: "Alice",

  address: {
    city: "London",
    country: "UK"
  }
};

const copy = {
  ...original
};

copy.address.city =
  "Manchester";

console.log(
  original.address.city
);

console.log(
  copy.address.city
);