List of 100 Javascript Coding Examples for Interview

Certainly! Here’s a curated list of 100 practical JavaScript coding examples commonly asked in technical interviews. These examples cover a wide range of topics, including algorithms, data structures, and core JavaScript concepts, to help you prepare effectively.

🔹 1–10: Basic JavaScript Concepts

Sum of Two Numbers
```
const add = (a, b) => a + b;
```

Check if a Number is Prime

const isPrime = num => num > 1 && ![...Array(num).keys()].slice(2).some(i => num % i === 0);

Factorial of a Number

const factorial = n => (n === 0 ? 1 : n * factorial(n - 1));

Fibonacci Series

const fibonacci = n => {
  let [a, b] = [0, 1];
  while (n--) {
    [a, b] = [b, a + b];
  }
  return a;
};

Reverse a String

const reverseString = str => str.split('').reverse().join('');

Palindrome Check

const isPalindrome = str => str === str.split('').reverse().join('');

Find Maximum in Array

const findMax = arr => Math.max(...arr);

Find Minimum in Array

const findMin = arr => Math.min(...arr);

Count Vowels in a String

const countVowels = str => (str.match(/[aeiou]/gi) || []).length;

Sum of Array Elements

const sumArray = arr => arr.reduce((acc, val) => acc + val, 0);

🔹 11–20: Array Manipulation

Array Rotation

const rotateArray = (arr, k) => [...arr.slice(k), ...arr.slice(0, k)];

Remove Duplicates from Array

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

Find Intersection of Two Arrays

const intersection = (arr1, arr2) => arr1.filter(value => arr2.includes(value));

Flatten Nested Array

const flattenArray = arr => arr.flat(Infinity);

Find Missing Number

const findMissing = arr => {
  const n = arr.length + 1;
  const total = (n * (n + 1)) / 2;
  return total - arr.reduce((acc, val) => acc + val, 0);
};

Shuffle Array

const shuffleArray = arr => arr.sort(() => Math.random() - 0.5);

Move Zeros to End

const moveZeros = arr => {
  const zeros = arr.filter(val => val === 0);
  const nonZeros = arr.filter(val => val !== 0);
  return [...nonZeros, ...zeros];
};

Chunk Array into Subarrays

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

Find First Non-Repeating Character

const firstNonRepeating = str => {
  for (let i = 0; i < str.length; i++) {
    if (str.indexOf(str[i]) === str.lastIndexOf(str[i])) {
      return str[i];
    }
  }
  return null;
};

Group Elements by Condition

const groupBy = (arr, condition) => {
  return arr.reduce((acc, item) => {
    const key = condition(item);
    if (!acc[key]) acc[key] = [];
    acc[key].push(item);
    return acc;
  }, {});
};

🔹 21–30: String Manipulation

Count Occurrences of a Character

const countChar = (str, char) => (str.match(new RegExp(char, 'g')) || []).length;

Capitalize First Letter of Each Word

const capitalizeWords = str => str.replace(/\b\w/g, char => char.toUpperCase());

Reverse Each Word in a Sentence

const reverseWords = str => str.split(' ').reverse().join(' ');

Longest Palindromic Substring

const longestPalindrome = str => {
  const expand = (left, right) => {
    while (left >= 0 && right < str.length && str[left] === str[right]) {
      left--;
      right++;
    }
    return str.slice(left + 1, right);
  };
  let result = '';
  for (let i = 0; i < str.length; i++) {
    const odd = expand(i, i);
    const even = expand(i, i + 1);
    const longer = odd.length > even.length ? odd : even;
    if (longer.length > result.length) result = longer;
  }
  return result;
};

Check Balanced Parentheses

const isBalanced = str => {
  const stack = [];
  const map = { '(': ')', '{': '}', '[': ']' };
  for (let char of str) {
    if (map[char]) {
      stack.push(char);
    } else if (Object.values(map).includes(char)) {
      if (map[stack.pop()] !== char) return false;
    }
  }
  return !stack.length;
};

Remove All Whitespace

const removeWhitespace = str => str.replace(/\s+/g, '');

Convert String to Title Case

const toTitleCase = str => str.replace(/\b\w/g, char => char.toUpperCase());

Find Longest Word in a Sentence

const longestWord = str => str.split(' ').reduce((longest, current) => current.length > longest.length ? current : longest, '');

Check if String Contains Only Digits

const isDigitsOnly = str => /^\d+$/.test(str);

Convert String to Number
```
const toNumber = str => Number(str);
```

🔹 31–40: Object Manipulation

Clone an Object

const cloneObject = obj => ({ ...obj });

Check Deep Equality of Two Objects

const isEqual = (a, b) => JSON.stringify(a) === JSON.stringify(b);

Merge Two Objects

const mergeObjects = (obj1, obj2) => ({ ...obj1, ...obj2 });

Invert Object Keys and Values

const invertObject = obj => Object.fromEntries(Object.entries(obj).map(([k, v]) => [v, k]));

Count Object Keys

const countKeys = obj => Object.keys(obj).length;

Convert Object to Array

const objToArray = obj => Object.entries(obj);

Convert Array to Object

const arrayToObj = arr => Object.fromEntries(arr);

Check if Object is Empty

const isEmpty = obj => Object.keys(obj).length === 0;

Access Nested Property

const getNested = (obj, path) => path.split('.').reduce((acc, part) => acc?.[part], obj);

Rename Object Key

const renameKey = (obj, oldKey, newKey) => {
  const { [oldKey]: old, ...rest } = obj;
  return { ...rest, [newKey]: old };
};

🔹 41–50: Math and Date

Get Random Number Between Two Values

const randomBetween = (min, max) => Math.floor(Math.random() * (max - min + 1)) + min;

Generate a Random Hex Color

const randomHex = () => '#' + Math.floor(Math.random() * 0xffffff).toString(16);

Convert Degrees to Radians

const degToRad = deg => deg * (Math.PI / 180);

Check Leap Year

const isLeapYear = year => (year % 4 === 0 && year % 100 !== 0) || year % 400 === 0;

Get Days Between Two Dates

const daysBetween = (d1, d2) => Math.abs((d2 - d1) / (1000 * 60 * 60 * 24));

Format Date to YYYY-MM-DD

const formatDate = date => date.toISOString().split('T')[0];

Get Current Time

const currentTime = () => new Date().toLocaleTimeString();

Add Days to Date

const addDays = (date, days) => new Date(date.setDate(date.getDate() + days));

Check if Date is Weekend

const isWeekend = date => [0, 6].includes(date.getDay());

Compare Two Dates

const isSameDate = (d1, d2) => d1.toDateString() === d2.toDateString();

🔹 51–70: Recursion and Iteration

Recursive Sum of Array

const sumRec = arr => arr.length === 0 ? 0 : arr[0] + sumRec(arr.slice(1));

Recursive Fibonacci

const fib = n => (n <= 1 ? n : fib(n - 1) + fib(n - 2));

Recursive Factorial

const factorial = n => (n <= 1 ? 1 : n * factorial(n - 1));

Print Numbers Using Recursion

const print = n => { if (n > 0) { console.log(n); print(n - 1); } };

Nested Object Traversal

const traverse = obj => {
  for (let key in obj) {
    if (typeof obj[key] === 'object') traverse(obj[key]);
    else console.log(key, obj[key]);
  }
};

Flatten Object

const flatten = (obj, prefix = '', res = {}) => {
  for (const k in obj) {
    const val = obj[k], pre = prefix.length ? `${prefix}.${k}` : k;
    if (typeof val === 'object') flatten(val, pre, res);
    else res[pre] = val;
  }
  return res;
};

Binary Search

const binarySearch = (arr, x) => {
  let l = 0, r = arr.length - 1;
  while (l <= r) {
    const mid = Math.floor((l + r) / 2);
    if (arr[mid] === x) return mid;
    x < arr[mid] ? r = mid - 1 : l = mid + 1;
  }
  return -1;
};

Bubble Sort

const bubbleSort = arr => {
  for (let i = 0; i < arr.length; i++)
    for (let j = 0; j < arr.length - i - 1; j++)
      if (arr[j] > arr[j + 1]) [arr[j], arr[j + 1]] = [arr[j + 1], arr[j]];
  return arr;
};

Quick Sort

const quickSort = arr => {
  if (arr.length < 2) return arr;
  const [pivot, ...rest] = arr;
  return [...quickSort(rest.filter(x => x <= pivot)), pivot, ...quickSort(rest.filter(x => x > pivot))];
};

Power Function

const power = (x, n) => n === 0 ? 1 : x * power(x, n - 1);

🔹 71–90: DOM and Events (Browser)

Get Element by ID

const el = document.getElementById('id');

Add Event Listener

document.querySelector('button').addEventListener('click', () => alert('Clicked'));

Change Inner Text

document.getElementById('demo').innerText = 'Hello';

Create Element

const div = document.createElement('div');
div.textContent = 'New';
document.body.appendChild(div);

Toggle Class

document.getElementById('box').classList.toggle('active');

Change Background Color

document.body.style.backgroundColor = 'lightblue';

Form Validation

document.querySelector('form').addEventListener('submit', e => {
  e.preventDefault();
  const input = document.querySelector('#name');
  if (input.value === '') alert('Name required');
});

Live Character Counter

document.querySelector('#input').addEventListener('input', e => {
  document.querySelector('#count').innerText = e.target.value.length;
});

Scroll to Top

window.scrollTo({ top: 0, behavior: 'smooth' });

Detect Key Press

document.addEventListener('keydown', e => console.log(`Key: ${e.key}`));

🔹 91–100: Miscellaneous

Debounce Function

const debounce = (fn, delay) => {
  let timeout;
  return (...args) => {
    clearTimeout(timeout);
    timeout = setTimeout(() => fn(...args), delay);
  };
};

Throttle Function

const throttle = (fn, delay) => {
  let last = 0;
  return (...args) => {
    const now = Date.now();
    if (now - last >= delay) {
      last = now;
      fn(...args);
    }
  };
};

Memoization

const memoize = fn => {
  const cache = {};
  return arg => (cache[arg] = cache[arg] || fn(arg));
};

Generate UUID

const uuid = () => 'xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx'.replace(/[xy]/g, c => {
  const r = Math.random() * 16 | 0;
  return (c === 'x' ? r : r & 0x3 | 0x8).toString(16);
});

Detect Type

const getType = val => Object.prototype.toString.call(val).slice(8, -1);

Deep Clone Object

const deepClone = obj => JSON.parse(JSON.stringify(obj));

Check if Array is Sorted

const isSorted = arr => arr.every((val, i, a) => i === 0 || a[i - 1] <= val);

Generate Range of Numbers

const range = (
start, end) => Array.from({ length: end - start + 1 }, (_, i) => i + start);

Convert Decimal to Binary

const toBinary = n => n.toString(2);

Convert Binary to Decimal

const toDecimal = bin => parseInt(bin, 2);

Blog

🔹 1–10: Basic JavaScript Concepts

🔹 11–20: Array Manipulation

🔹 21–30: String Manipulation

🔹 31–40: Object Manipulation

🔹 41–50: Math and Date

🔹 51–70: Recursion and Iteration

🔹 71–90: DOM and Events (Browser)

🔹 91–100: Miscellaneous

Leave a Reply Cancel reply

Javascript: List of 100 Javascript Coding Examples for Interview

🔹 1–10: Basic JavaScript Concepts

🔹 11–20: Array Manipulation

🔹 21–30: String Manipulation

🔹 31–40: Object Manipulation

🔹 41–50: Math and Date

🔹 51–70: Recursion and Iteration

🔹 71–90: DOM and Events (Browser)

🔹 91–100: Miscellaneous

Leave a Reply Cancel reply