Bubble popper

Use jQuery & CSS animations and transitions to make a small application that makes and pops random bubbles.


We’ll have a fully functional application that—when the space key is pressed—makes a random, poppable bubble.

This is what it should look like when it’s done:

  1. Type it, type it real good

    Remember the purpose of this lesson is to type the code out yourself—build up that muscle memory in your fingers!

Fork & clone

Start the lesson by forking and cloning the bubble-popper repository.

Fork & clone the “bubble-popper” repo.

The repository will have some starter files to get you on your way and include requirements for Markbot so you can be sure you’ve completed the lesson.

  1. Fork, clone & Markbot

    This includes some starter code that you can get by forking and cloning the repository. You’ll use Markbot to double check everything is done properly.

1 Set up project

Before we get started, create some files and get ready.

  1. bubble-popper
  2. index.html
  3. css
  4. main.css
  5. js
  6. main.js
  1. Make an index.html & add the boilerplate code.
  2. Make a main.css in your css folder & add the boilerplate code.
  3. Make an empty main.js in your js folder & connect it to your HTML.
  4. Connect jQuery to your website, with the URL from cdnjs.
  1. Naming conventions

    Don’t forget to follow the naming conventions.

2 HTML setup

We’re not going to need any HTML elements to make this work, so the <body> can stay empty except for the <script> tags.

<!DOCTYPE html>
<html lang="en-ca">
  <meta charset="utf-8">
  <title>Bubble popper</title>
  <meta name="viewport" content="width=device-width,initial-scale=1">
  <link href="css/main.css" rel="stylesheet">

  <script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.2.1/jquery.min.js"></script>
  <script src="js/main.js"></script>
  1. HTML snippets

    Create the boilerplate with html5, viewport, css & jss

  2. Line K

    Don’t forget to hook up jQuery.

3 Styling the bubbles

With a touch of CSS we can transform any <div> into a bubble.

html {
  box-sizing: border-box;

*, *::before, *::after {
  box-sizing: inherit;

.bubble {
  left: 0;
  top: 0;
  position: absolute;
  height: 50px;
  width: 50px;
  border-radius: 50%;
  background-color: lightblue;
  1. CSS snippets

    Create the boilerplate with borderbox

  2. Lines J–L

    Using position: absolute is really important here because we want to be able to the move the circle around the screen with coordinates.

4 Add random bubbles to the screen

When the Space key is pressed on the keyboard, we’re going to create a new <div> tag, with the class of bubble, and place it on the screen in a random location.

var $body = $('body');

$('html').on('keydown', function (e) {
  var $bubble;

  if (e.key == ' ') {
    $bubble = $('<div>');
      'top': Math.random() * (document.documentElement.clientHeight - 100),
      'left': Math.random() * (document.documentElement.clientWidth - 100)

At this point, pressing the Space key should create a random bubble on the screen.

  1. Line F

    The Space key is represented by the key ' ' a literal space. You can see all the different key values here.

  2. Line I

    If we want to change multiple CSS properties at the same time we can pass and object to the .css() function instead of calling it multiple times.

  3. Lines J–K

    We can use document.documentElement.clientWidth & height to constrain the random coordinates to the dimensions of the window.

    The - 100 here is subtracting the width of the circle so they don’t appear slightly off the screen.

5 Make the bubbles grow

When the bubbles appear on the screen, it’d be neat if they grew into place. With some CSS animations we can do that.

.bubble {
  border-radius: 50%;
  background-color: lightblue;
  animation: bounce .5s cubic-bezier(.5, -.9, .6, 1.9) forwards;
  transform: translate(-50%, -50%);

@keyframes bounce {
  0% {
    height: 50px;
    width: 50px;
  100% {
    height: 100px;
    width: 100px;

With a refresh in your browser, pressing Space now should drop a bubble on the screen and it should animate.

  1. Line E

    Add an animation to the bubble that makes a bounce effect.

    Notice in the keyframes that the bubble is just being scaled from 50px to 100px. The bouncing comes from the custom easing: cubic-bezier()

    With the cubic-bezier() function we can make any kind of easing we want. I didn’t magically come up with these numbers I used a cubic bezier generator.

    We’re using forwards here to keep the bubble at its bigger size when it’s done animating, otherwise it would snap back to the smaller size.

  2. Line F

    The transform is here so the bubble scales from the centre, because we’re adjusting the width and height it will naturally scale from the top-left corner, so we’re changing the anchor point.

    Of course, I could have used transform: scale() inside @keyframes instead of width & height to acheive the same results.

6 Click to pop

The next piece of code we’re going to write is to make the bubbles “pop” when they are clicked.

To start, let’s write some JavaScript that will add a class to the bubble when it’s clicked:


$body.on('click', '.bubble', function () {
  1. Line F

    We’re using event delegation here: listening for clicks on the <body>, but only activating the event handler when a .bubble is called upon.

    We need to use event delegation because we don’t know how many bubbles there are and we don’t want to add an event listener to every single one.

7 Popping CSS

The new .is-popping class will change the width & height to 0, making the bubble shrink & set the opacity to 0 to fade the bubble away.

We also need to add a transition to the .bubble to create the easing effect.

.bubble {
  animation: bounce .5s cubic-bezier(.5, -.9, .6, 1.9) forwards;
  transform: translate(-50%, -50%);
    width .3s cubic-bezier(.7, -.6, .4, 1.5),
    height .3s cubic-bezier(.7, -.6, .4, 1.5),
    opacity .3s ease-out

.is-popping {
  height: 0;
  width: 0;
  opacity: 0;
  animation-name: none;

@keyframes bounce {
  0% {
    height: 50px;

When clicking on each of the bubbles now they should shrink and fade away.

  1. Lines E–I

    The transition is written on multiple lines because certain properties are going to have different easing than others—and one line is difficult to read.

    The 3 different transitions:

    • The width & height should have a bouncing effect
    • The opactiy should just ease-out
  2. Line P

    It’s very important that we remove the animation at this point. Because the forwards in the animation forces the element to stay at its largest size after the animation is completed.

    Without removing the animation from the element we wouldn’t see it shrink.

8 Removing the element when completed

Even though the bubble shrinks and fades away there’s still an invisible <div> in the HTML.

Let’s use JavaScript to remove the <div> from the <body> after its animation has finished:


$body.on('transitionend', '.bubble', function () {
  1. Line E

    The code is listening for the transitionend event that will be triggered whenever the .bubble has finished its shrinking-fading transition.

  2. Line F

    We then target $(this)—which represents the single ball that finished—and remove it from the <body>

Drop it into Markbot & submit

Drop the final, coded exercise into Markbot and fix all the errors until Markbot gives you all green (and maybe a little yellow).

After you’ve fixed all the problems, go ahead and submit the assignment. You’ll immediately get your grade.

  1. Submit

    Whenever you’ve passed all Markbot’s specific tests go ahead and submit this lesson for marks.