JavaScript Snippet Library Free Online Tool 2026

Last updated March 22, 2026

JavaScript Snippet Library Examples

The JavaScript Snippet Library provides ready-to-use, tested code snippets for common programming tasks. Below are examples from the library's main categories.

Array Manipulation Snippets

// Remove duplicates from array
const unique = arr => [...new Set(arr)];
unique([1, 2, 2, 3, 3, 4]);  // → [1, 2, 3, 4]

// Flatten nested array
const flatten = arr => arr.flat(Infinity);
flatten([1, [2, [3, [4]]]]);  // → [1, 2, 3, 4]

// Group array by property
const groupBy = (arr, key) =>
  arr.reduce((groups, item) => ({
    ...groups,
    [item[key]]: [...(groups[item[key]] || []), item]
  }), {});

groupBy([
  { name: 'Alice', dept: 'Engineering' },
  { name: 'Bob',   dept: 'Marketing' },
  { name: 'Carol', dept: 'Engineering' }
], 'dept');
// → { Engineering: [{Alice}, {Carol}], Marketing: [{Bob}] }

// Array intersection
const intersection = (a, b) => a.filter(x => b.includes(x));
intersection([1, 2, 3, 4], [2, 4, 6]);  // → [2, 4]

// Shuffle array (Fisher-Yates)
const shuffle = arr => {
  const a = [...arr];
  for (let i = a.length - 1; i > 0; i--) {
    const j = Math.floor(Math.random() * (i + 1));
    [a[i], a[j]] = [a[j], a[i]];
  }
  return a;
};

String Processing Snippets

// Truncate string with ellipsis
const truncate = (str, maxLen) =>
  str.length > maxLen ? str.slice(0, maxLen - 3) + '...' : str;
truncate('Hello, World!', 8);  // → "Hello..."

// Convert to camelCase
const toCamelCase = str =>
  str.replace(/[-_\s]+(.)/g, (_, c) => c.toUpperCase());
toCamelCase('hello-world');    // → "helloWorld"
toCamelCase('foo_bar_baz');    // → "fooBarBaz"

// Convert to kebab-case
const toKebabCase = str =>
  str.replace(/([a-z])([A-Z])/g, '$1-$2')
     .replace(/[\s_]+/g, '-')
     .toLowerCase();
toKebabCase('helloWorld');     // → "hello-world"
toKebabCase('FooBarBaz');      // → "foo-bar-baz"

// Count word occurrences
const wordCount = str =>
  str.trim().split(/\s+/).reduce((counts, word) => ({
    ...counts,
    [word.toLowerCase()]: (counts[word.toLowerCase()] || 0) + 1
  }), {});
wordCount('the cat sat on the mat');
// → { the: 2, cat: 1, sat: 1, on: 1, mat: 1 }

// Generate random string
const randomString = (len = 8) =>
  Math.random().toString(36).substring(2, 2 + len);
randomString(6);  // → "k3m9xp"

Date and Time Snippets

// Format date as YYYY-MM-DD
const formatDate = date =>
  date.toISOString().split('T')[0];
formatDate(new Date());  // → "2024-01-15"

// Days between two dates
const daysBetween = (d1, d2) =>
  Math.abs(Math.round((d2 - d1) / (1000 * 60 * 60 * 24)));
daysBetween(new Date('2024-01-01'), new Date('2024-01-15'));  // → 14

// Add days to date
const addDays = (date, days) => {
  const result = new Date(date);
  result.setDate(result.getDate() + days);
  return result;
};
addDays(new Date('2024-01-15'), 30);  // → 2024-02-14

// Check if date is in the past
const isPast = date => date < new Date();

// Relative time (time ago)
const timeAgo = date => {
  const seconds = Math.floor((new Date() - date) / 1000);
  const intervals = [
    [31536000, 'year'], [2592000, 'month'],
    [86400, 'day'], [3600, 'hour'],
    [60, 'minute'], [1, 'second']
  ];
  for (const [secs, label] of intervals) {
    const count = Math.floor(seconds / secs);
    if (count >= 1) return `${count} ${label}${count > 1 ? 's' : ''} ago`;
  }
  return 'just now';
};
timeAgo(new Date(Date.now() - 3600000));  // → "1 hour ago"

DOM Manipulation Snippets

// Check if element is in viewport
const isInViewport = el => {
  const rect = el.getBoundingClientRect();
  return (
    rect.top >= 0 &&
    rect.left >= 0 &&
    rect.bottom <= window.innerHeight &&
    rect.right <= window.innerWidth
  );
};

// Smooth scroll to element
const scrollTo = el =>
  el.scrollIntoView({ behavior: 'smooth', block: 'start' });

// Copy text to clipboard
const copyToClipboard = text =>
  navigator.clipboard.writeText(text);

// Detect device type
const isMobile = () => window.innerWidth < 768;
const isTablet = () => window.innerWidth >= 768 && window.innerWidth < 1024;
const isDesktop = () => window.innerWidth >= 1024;

// Get all query parameters
const getQueryParams = () =>
  Object.fromEntries(new URLSearchParams(window.location.search));
// URL: ?name=Alice&age=30
// → { name: 'Alice', age: '30' }

Async Utility Snippets

// Debounce
const debounce = (fn, delay) => {
  let timer;
  return (...args) => {
    clearTimeout(timer);
    timer = setTimeout(() => fn(...args), delay);
  };
};
const debouncedSearch = debounce(search, 300);

// Throttle
const throttle = (fn, limit) => {
  let lastCall = 0;
  return (...args) => {
    const now = Date.now();
    if (now - lastCall >= limit) {
      lastCall = now;
      return fn(...args);
    }
  };
};
const throttledScroll = throttle(handleScroll, 100);

// Retry with exponential backoff
const retry = async (fn, retries = 3, delay = 1000) => {
  try {
    return await fn();
  } catch (err) {
    if (retries === 0) throw err;
    await new Promise(r => setTimeout(r, delay));
    return retry(fn, retries - 1, delay * 2);
  }
};

// Sleep / delay
const sleep = ms => new Promise(resolve => setTimeout(resolve, ms));
await sleep(1000);  // wait 1 second

// Run async tasks with concurrency limit
const asyncPool = async (limit, tasks) => {
  const results = [];
  const executing = new Set();
  for (const task of tasks) {
    const p = Promise.resolve().then(task);
    results.push(p);
    executing.add(p);
    p.finally(() => executing.delete(p));
    if (executing.size >= limit) await Promise.race(executing);
  }
  return Promise.all(results);
};

Object Utility Snippets

// Deep clone object
const deepClone = obj => JSON.parse(JSON.stringify(obj));

// Deep merge objects
const deepMerge = (target, source) => {
  const result = { ...target };
  for (const key of Object.keys(source)) {
    if (source[key] instanceof Object && !Array.isArray(source[key])) {
      result[key] = deepMerge(target[key] || {}, source[key]);
    } else {
      result[key] = source[key];
    }
  }
  return result;
};

// Pick specific keys from object
const pick = (obj, keys) =>
  Object.fromEntries(keys.map(k => [k, obj[k]]));
pick({ a: 1, b: 2, c: 3 }, ['a', 'c']);  // → { a: 1, c: 3 }

// Omit keys from object
const omit = (obj, keys) =>
  Object.fromEntries(Object.entries(obj).filter(([k]) => !keys.includes(k)));
omit({ a: 1, b: 2, c: 3 }, ['b']);  // → { a: 1, c: 3 }

Browse the full library by category or search by keyword to find the right snippet for your task. Each snippet includes browser compatibility notes and usage examples.