Pen Settings



CSS Base

Vendor Prefixing

Add External Stylesheets/Pens

Any URL's added here will be added as <link>s in order, and before the CSS in the editor. If you link to another Pen, it will include the CSS from that Pen. If the preprocessor matches, it will attempt to combine them before processing.

+ add another resource


Babel is required to process package imports. If you need a different preprocessor remove all packages first.

Add External Scripts/Pens

Any URL's added here will be added as <script>s in order, and run before the JavaScript in the editor. You can use the URL of any other Pen and it will include the JavaScript from that Pen.

+ add another resource


Save Automatically?

If active, Pens will autosave every 30 seconds after being saved once.

Auto-Updating Preview

If enabled, the preview panel updates automatically as you code. If disabled, use the "Run" button to update.

Format on Save

If enabled, your code will be formatted when you actively save your Pen. Note: your code becomes un-folded during formatting.

Editor Settings

Code Indentation

Want to change your Syntax Highlighting theme, Fonts and more?

Visit your global Editor Settings.


                <!-- animation container -->
<h2 class="animation-title">Frame by Frame Animation (JavaScript)</h2>
<img class="eye-animation" 
   alt="blinking eye animation"/>


                // animation container
.animation-title {
  font-family: sans-serif;
  text-align: center;
.eye-animation {
  width: 300px;
  display: block;
  // place in the middle of the screen
  margin: auto; 


                const $element = $('.eye-animation');
const imagePath = '';
const totalFrames = 18;
const animationDuration = 1300;
const timePerFrame = animationDuration / totalFrames;
let timeWhenLastUpdate;
let timeFromLastUpdate;
let frameNumber = 1;

// 'step' function will be called each time browser rerender the content
// we achieve that by passing 'step' as a parameter to the 'requestAnimationFrame' function
function step(startTime) {
  // 'startTime' is provided by requestAnimationName function, and we can consider it as current time
  // first of all we calculate how much time has passed from the last time when frame was update
  if (!timeWhenLastUpdate) timeWhenLastUpdate = startTime;
  timeFromLastUpdate = startTime - timeWhenLastUpdate;
  // then we check if it is time to update the frame
  if (timeFromLastUpdate > timePerFrame) {
    // and update it accordingly
    $element.attr('src', imagePath + `/Eye-${frameNumber}.svg`);
    // reset the last update time
    timeWhenLastUpdate = startTime;
    // then increase the frame number or reset it if it is the last frame
    if (frameNumber >= totalFrames) {
      frameNumber = 1;
    } else {
      frameNumber = frameNumber + 1;

// create a set of hidden divs
// and set their background-image attribute to required images
// that will force browser to download the images
$(document).ready(() => {
  for (var i = 1; i < totalFrames + 1; i++) {
    $('body').append(`<div id="preload-image-${i}" style="background-image: url('${imagePath}/Eye-${i}.svg');"></div>`);

// wait for images to be downloaded and start the animation
$(window).on('load', () => {