24 modern ES6 code snippets to solve practical JS problems

I hand-picked some of the most useful code snippets from 30 seconds of code. It's an awesome resource, go ahead and show it some ❤️.

In this article I tried to sorted them based on their practical use, answering common questions you may face in your project:

1.How to hide all elements specified?

const hide = (...el) => [...el].forEach(e => (e.style.display = 'none'));

// Example
hide(document.querySelectorAll('img')); // Hides all <img> elements on the page

2.How to check if the element has the specified class?

const hasClass = (el, className) => el.classList.contains(className);

// Example
hasClass(document.querySelector('p.special'), 'special'); // true

3.How to toggle a class for an element?

const toggleClass = (el, className) => el.classList.toggle(className);

// Example
toggleClass(document.querySelector('p.special'), 'special'); 
// The paragraph will not have the 'special' class anymore

4.How to get the scroll position of the current page?

const getScrollPosition = (el = window) => ({
  x: el.pageXOffset !== undefined ? el.pageXOffset : el.scrollLeft,
  y: el.pageYOffset !== undefined ? el.pageYOffset : el.scrollTop
});

// Example
getScrollPosition(); // {x: 0, y: 200}

5.How to smooth-scroll to the top of the page?

const scrollToTop = () => {
  const c = document.documentElement.scrollTop || document.body.scrollTop;
  if (c > 0) {
    window.requestAnimationFrame(scrollToTop);
    window.scrollTo(0, c - c / 8);
  }
};

// Example
scrollToTop();

6.How to check if the parent element contains the child element?

const elementContains = (parent, child) => parent !== child && parent.contains(child);

// Examples
elementContains(document.querySelector('head'), document.querySelector('title')); 
// true
elementContains(document.querySelector('body'), document.querySelector('body')); // false

7.How to check if the element specified is visible in the viewport?

const elementIsVisibleInViewport = (el, partiallyVisible = false) => {
  const { top, left, bottom, right } = el.getBoundingClientRect();
  const { innerHeight, innerWidth } = window;
  return partiallyVisible
    ? ((top > 0 && top < innerHeight) || (bottom > 0 && bottom < innerHeight)) &&
        ((left > 0 && left < innerWidth) || (right > 0 && right < innerWidth))
    : top >= 0 && left >= 0 && bottom <= innerHeight && right <= innerWidth;
};

// Examples
elementIsVisibleInViewport(el); // (not fully visible)
elementIsVisibleInViewport(el, true); // (partially visible)

8.How to fetch all images within an element?

const getImages = (el, includeDuplicates = false) => {
  const images = [...el.getElementsByTagName('img')].map(img => img.getAttribute('src'));
  return includeDuplicates ? images : [...new Set(images)];
};

// Examples
getImages(document, true); // ['image1.jpg', 'image2.png', 'image1.png', '...']
getImages(document, false); // ['image1.jpg', 'image2.png', '...']

9.How to figure out if the device is a mobile device or a desktop/laptop?

const detectDeviceType = () =>
  /Android|webOS|iPhone|iPad|iPod|BlackBerry|IEMobile|Opera Mini/i.test(navigator.userAgent)
    ? 'Mobile'
    : 'Desktop';

// Example
detectDeviceType(); // "Mobile" or "Desktop"

10.How to get the current URL?

const currentURL = () => window.location.href;

// Example
currentURL(); // 'https://google.com'

11.How to create an object containing the parameters of the current URL?

const getURLParameters = url =>
  (url.match(/([^?=&]+)(=([^&]*))/g) || []).reduce(
    (a, v) => ((a[v.slice(0, v.indexOf('='))] = v.slice(v.indexOf('=') + 1)), a),
    {}
  );

// Examples
getURLParameters('http://url.com/page?n=Adam&s=Smith'); // {n: 'Adam', s: 'Smith'}
getURLParameters('google.com'); // {}

12.How to encode a set of form elements as an object?

const formToObject = form =>
  Array.from(new FormData(form)).reduce(
    (acc, [key, value]) => ({
      ...acc,
      [key]: value
    }),
    {}
  );

// Example
formToObject(document.querySelector('#form')); // { email: '[e-mail]', name: 'Test Name' }

13.How to retrieve a set of properties indicated by the given selectors from an object?

const get = (from, ...selectors) =>
  [...selectors].map(s =>
    s
      .replace(/\[([^\[\]]*)\]/g, '.$1.')
      .split('.')
      .filter(t => t !== '')
      .reduce((prev, cur) => prev && prev[cur], from)
  );
const obj = { selector: { to: { val: 'val to select' } }, target: [1, 2, { a: 'test' }] };

// Example
get(obj, 'selector.to.val', 'target[0]', 'target[2].a'); // ['val to select', 1, 'test']

14.How to invoke the provided function after wait (in milliseconds)?

const delay = (fn, wait, ...args) => setTimeout(fn, wait, ...args);
delay(
  function(text) {
    console.log(text);
  },
  1000,
  'later'
); 

// Logs 'later' after one second.

15.How to trigger a specific event on a given element, optionally passing custom data?

const triggerEvent = (el, eventType, detail) =>
  el.dispatchEvent(new CustomEvent(eventType, { detail }));

// Examples
triggerEvent(document.getElementById('myId'), 'click');
triggerEvent(document.getElementById('myId'), 'click', { username: 'bob' });

16.How to remove an event listener from an element?

const off = (el, evt, fn, opts = false) => el.removeEventListener(evt, fn, opts);

const fn = () => console.log('!');
document.body.addEventListener('click', fn);
off(document.body, 'click', fn); // no longer logs '!' upon clicking on the page

17.How to get readable format of the given number of milliseconds?

const formatDuration = ms => {
  if (ms < 0) ms = -ms;
  const time = {
    day: Math.floor(ms / 86400000),
    hour: Math.floor(ms / 3600000) % 24,
    minute: Math.floor(ms / 60000) % 60,
    second: Math.floor(ms / 1000) % 60,
    millisecond: Math.floor(ms) % 1000
  };
  return Object.entries(time)
    .filter(val => val[1] !== 0)
    .map(([key, val]) => `${val} ${key}${val !== 1 ? 's' : ''}`)
    .join(', ');
};

// Examples
formatDuration(1001); // '1 second, 1 millisecond'
formatDuration(34325055574); // '397 days, 6 hours, 44 minutes, 15 seconds, 574 milliseconds'

18.How to get the difference (in days) between two dates?

const getDaysDiffBetweenDates = (dateInitial, dateFinal) =>
  (dateFinal - dateInitial) / (1000 * 3600 * 24);

// Example
getDaysDiffBetweenDates(new Date('2017-12-13'), new Date('2017-12-22')); // 9

19.How to make a GET request to the passed URL?

const httpGet = (url, callback, err = console.error) => {
  const request = new XMLHttpRequest();
  request.open('GET', url, true);
  request.onload = () => callback(request.responseText);
  request.onerror = () => err(request);
  request.send();
};

httpGet(
  'https://jsonplaceholder.typicode.com/posts/1',
  console.log
); 

// Logs: {"userId": 1, "id": 1, "title": "sample title", "body": "my text"}

20.How to make a POST request to the passed URL?

const httpPost = (url, data, callback, err = console.error) => {
  const request = new XMLHttpRequest();
  request.open('POST', url, true);
  request.setRequestHeader('Content-type', 'application/json; charset=utf-8');
  request.onload = () => callback(request.responseText);
  request.onerror = () => err(request);
  request.send(data);
};

const newPost = {
  userId: 1,
  id: 1337,
  title: 'Foo',
  body: 'bar bar bar'
};
const data = JSON.stringify(newPost);
httpPost(
  'https://jsonplaceholder.typicode.com/posts',
  data,
  console.log
); 

// Logs: {"userId": 1, "id": 1337, "title": "Foo", "body": "bar bar bar"}

21.How to create a counter with the specified range, step and duration for the specified selector?

const counter = (selector, start, end, step = 1, duration = 2000) => {
  let current = start,
    _step = (end - start) * step < 0 ? -step : step,
    timer = setInterval(() => {
      current += _step;
      document.querySelector(selector).innerHTML = current;
      if (current >= end) document.querySelector(selector).innerHTML = end;
      if (current >= end) clearInterval(timer);
    }, Math.abs(Math.floor(duration / (end - start))));
  return timer;
};

// Example
counter('#my-id', 1, 1000, 5, 2000); // Creates a 2-second timer for the element with id="my-id"

22.How to copy a string to the clipboard?

const copyToClipboard = str => {
  const el = document.createElement('textarea');
  el.value = str;
  el.setAttribute('readonly', '');
  el.style.position = 'absolute';
  el.style.left = '-9999px';
  document.body.appendChild(el);
  const selected =
    document.getSelection().rangeCount > 0 ? document.getSelection().getRangeAt(0) : false;
  el.select();
  document.execCommand('copy');
  document.body.removeChild(el);
  if (selected) {
    document.getSelection().removeAllRanges();
    document.getSelection().addRange(selected);
  }
};

// Example
copyToClipboard('Lorem ipsum'); // 'Lorem ipsum' copied to clipboard.

23.How to find out if the browser tab of the page is focused?

const isBrowserTabFocused = () => !document.hidden;

// Example
isBrowserTabFocused(); // true

24.How to create a directory, if it does not exist?

const fs = require('fs');
const createDirIfNotExists = dir => (!fs.existsSync(dir) ? fs.mkdirSync(dir) : undefined);

// Example
createDirIfNotExists('test'); // creates the directory 'test', if it doesn't exist

---

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Comments

[Ibrahim Ezzy]

hasClass(document.querySelector('p.special'), 'special'); doesn't make sense. If you're already searching with the class in selector, couldn't you just do if (document.querySelector('p.special')) ?

[fetishlace]

To point 12.
Instead of confusing reduce I would do rather:
const formToObject = form => Object.fromEntries([...new FormData(form)])
(when Object.fromEntries() is available indeed...)

[Dima]

Congrat, you reinvented
yarn add jquery

[Jscripter]

I didn't know about the classList.toggle. Thanks.
In nodejs there is native package called querystring for url parameters.
I find it useful copy to clipboard, used it in a project.

[Heiker]

const delay = (fn, wait, ...args) => setTimeout(fn, wait, ...args);

That number 14 really doesn't do anything. You might as well just assign the function to delay.

const delay = setTimeout;

[Madza]

I see your point. This is great for hard-coded values in setTimeout() method and without need to create other constants later, like:

const delay = setTimout(()=>{console.log('delay event')}, 1000); 
// logs 'delay event' after 1000ms each time

by wrapping setTimeout() method in a function you can re-use your defined timer function with different values each time without creating new constants:

const delay = (fn, wait, ...args) => setTimeout(fn, wait, ...args);
delay(()=>{console.log('delay event 1')}, 1000) //logs 'delay event 1' after 1000ms
delay(()=>{console.log('delay event 2')}, 5000) //logs 'delay event 2' after 5000ms, etc

[Heiker]

by wrapping setTimeout() method in a function you can re-use your defined timer function with different values each time without creating new constants

I'm not sure I understand what you're saying here. They behave the same.

var delay = (fn, wait, ...args) => setTimeout(fn, wait, ...args);
var renamed = setTimeout;

var handler = (arg) => { console.log('delay event 1', arg) };
var other_handler = (arg) => { console.log('another one', arg) };

delay(handler, 1000, 'from delay');
renamed(handler, 1000, 'from renamed');
setTimeout(handler, 1000, 'from setTimeout');

delay(other_handler, 2000, 'from delay');
renamed(other_handler, 2000, 'from renamed');
setTimeout(other_handler, 2000, 'from setTimeout');

---

Personally, if I were to wrap setTimeout it would be to change the function signature, something like this.

var delay_fn = (wait, fn) => (...args) => setTimeout(fn, wait, ...args);

var delay_log = delay_fn(1000, handler);

delay_log('from delay log');

I only use var because I tested these on firefox's devtools.

[Madza]

That's the point - they behave the same, but you don't have to create new variables for the same functionality throughout your app. Instead you just use the same function once you need timer functionality for something.

Furthermore, if you need different function signature, you can use the latter assigning it to different var.

[Heiker]

they behave the same, but you don't have to create new variables for the same functionality throughout your app.

if I assign setTimeout that will force me to create new unnecesary variables in the entire app? And that doesn't happen if I wrap it in a function?

[Denis Efremov]

/**
 * Sleep pause.
 *
 * @param {Number} time The time in milliseconds.
 * @return {Promise<void>}
 */
const sleep = (time) => new Promise((resolve) => {
  setTimeout(resolve, time)
})

[Andrea Giammarchi]

The getURLParameters is not really safe/useful, I'd go instead with:

const getURLParameters = url => [
  ...new URL(url).searchParams
].reduce(
  (obj, [key, value]) => ((obj[key] = value), obj),
  {}
);

or, for possible duplicated keys:

const getURLParameters = url => [
  ...new URL(url).searchParams
].reduce(
  (obj, [key, value]) => ((
    obj[key] = key in obj ? [].concat(obj[key], value) : value
  ), obj),
  Object.create(null)
);

[Ibrahim Ezzy]

To to check if the element specified is visible in the viewport, IntersectionObserver is more performant and available in all major browsers.

[Madza]

Thanks for your feed. Checked in caniuse and the support is better than i expected :)

[thedevkim]

I love one liners but I'm afraid that my co-developers wont get it right.

[Madza]

For those not familiar with ES6 syntax it could be harder to grasp at first :)

[Clint Buhs]

Yeah, but these aren't one liners in the traditional sense (code crushed like a soda can for no good reason). The new syntax is worth working to understand since it brings benefits beyond brevity.

[Marko]

22 can be shortened a lot. Here is shorter version.

const listener = (e: ClipboardEvent) => {
  e.clipboardData.setData('text/plain', text);
  e.preventDefault();
};

document.addEventListener('copy', listener);
document.execCommand('copy');
document.removeEventListener('copy', listener);

[Madza]

Thanks for your point. I first started with clipbard.js for that (3kb gzipped) :)

[Denis Efremov]

const hide = (...el) => [...el].forEach(e => (e.style.display = 'none'));

This is wrong! ^

const hide = (el) => [...el].forEach(e => (e.style.display = 'none')); 

This is correct! ^