by Marina Ferreira
Learn JS, CSS and HTML by building a memory game in 30 minutes!
- ?Demo: Memory Game Project
Let’s start creating the files in the terminal:
? mkdir memory-game ? cd memory-game ? touch index.html styles.css scripts.js ? mkdir img
The initial template linking both
The game has 12 cards. Each card consists of a container
.memory-card, which holds two
img elements. The first one represents the card
front-face and the second its
You can download the assets for this project at: Memory Game Repo.
The set of cards will be wrapped in a
section container element. The final result:
We will use a simple but yet very useful reset, applied to all items:
box-sizing: border-box property includes padding and border values into element’s total width and height, so we can skip the math.
By setting display: flex to the
margin: auto to the
.memory-game container, it will be centered both vertically and horizontally.
.memory-game will also be a
flex-container. By default, the items are set to shrink in width to fit the container. By setting flex-wrap to
flex-items wrap along multiple lines, accordingly to their size.
height is calculated with calc() CSS function. Let’s make three rows, four card each by setting
.memory-card children, let’s add
position: relative so we can position the children absolutely, relative to it.
position: absolute set to both
back-face, will remove the elements from the original position, and stack them on top of each other.
The template should be looking like this:
Let’s also add a click effect. The
:active pseudo class will be triggered every time the element gets clicked. It will apply a .2s transition to its size:
To flip the card when clicked, a class
flip is added to the element. For that, let’s select all
memory-card elements with
document.querySelectorAll. Then loop through them with
forEach and attach an event listener. Every time a card gets clicked
flipCard function will be fired. The
this variable represents the card that was clicked. The function accesses the element’s
classList and toggles the
In the CSS the
flip class rotates the card 180deg:
To produce the 3D flip effect, we will add the perspective property to
.memory-game. That property sets how far in the
z plane the object is from the user. The lower the value the bigger the perspective effect. For a subtle effect, let’s apply
.memory-card elements let’s add
transform-style: preserve-3d, to position them in the 3D space created in the parent, instead of flattening it to the
z = 0 plane (transform-style).
Now, a transition has to be applied to the
transform property to produce the movement effect:
So, we got the card to 3D flip, yay! But why isn’t the card face showing up? Right now, both
.back-face are stacked up onto each other, because they are absolutely positioned. Every element has a
back face, which is a mirror image of its
front face. The property backface-visibility defaults to
visible, so when we flip the card, what we get is the JS badge back face.
To reveal the image underneath it, let’s apply
backface-visibility: hidden to
If we refresh the page and flip a card, it’s gone!
Since we’ve hidden both images back face, there is nothing in the other side. So now we have to turn the
.front-face 180 degrees:
And now, there’s the desired flip effect!
Now that we have flipping cards, let’s handle the matching logic.
When we click the first card, it needs to wait until another card is flipped. The variables
flippedCard will manage the flip state. In case there is no card flipped,
hasFlippedCard is set to
flippedCard is set to the clicked card. Let’s also switch the
toggle method to
So now, when the user clicks the second card, we will fall into the else block in our condition. We will check to see if it’s a match. In order to do that, let’s identify each card.
Whenever we feel like adding extra information to HTML elements, we can make use of data attributes. By using the following syntax:
* can be any word, that attribute will be inserted in the element’s dataset property. So, let’s add a
data-framework to each card:
So now we can check for a match by accessing both cards dataset. Let’s extract the matching logic to its own method
checkForMatch() and also set
hasFlippedCard back to false. In case of a match,
disableCards() is invoked and the event listeners on both cards are detached, to prevent further flipping. Otherwise,
unflipCards() will turn both cards back by a 1500ms timeout that removes the
Putting all together:
A more elegant way of writing the matching condition is to use a ternary operator. It’s composed by three blocks. The first block is the condition to be evaluated. The second block is executed if the condition returns true, otherwise the executed block is the third:
So now that we have the matching logic covered, we need to lock the board. We lock the board to avoid two sets of cards being turned at the same time, otherwise the flipping will fail.
Let’s declare a
lockBoard variable. When the player clicks the second card,
lockBoard will be set to
true and the condition
if (lockBoard) return; will prevent any card flipping before the cards are hidden or match:
Same Card Click
The is still the case where the player can click twice on the same card. The matching condition would evaluate to true, removing the event listener from that card.
To prevent that, let’s check if the current clicked card is equal to the
firstCard and return if positive.
secondCard variables need to be reset after each round, so let’s extract that to a new method
resetBoard(). Let’s place the
hasFlippedCard = false; and
lockBoard = false there too. The es6 destructuring assignment
[var1, var2] = ['value1', 'value2'], allows us to keep the code super short:
The new method will be called both from
Our game looks pretty good, but there is no fun if the cards are not shuffled, so let’s take care of that now.
display: flex is declared on the container,
flex-items are arranged by the following hierarchy: group and source order. Each group is defined by the order property, which holds a positive or negative integer. By default, each
flex-item has its
order property set to
0, which means they all belong to the same group and will be laid out by source order. If there is more than one group, elements are firstly arranged by ascending group order.
There is 12 cards in the game, so we will iterate through them, generate a random number between 0 and 12 and assign it to the flex-item
In order to invoke the
shuffle function, let’s make it a Immediately Invoked Function Expression (IIFE), which means it will execute itself right after its declaration. The scripts should look like this:
And that’s all folks!
You can also find a video explanation at ? Code Sketch Channel.
Marina Ferreira — Flexbox Fundamentals
MDN Web Docs — Main Axis
MDN Web Docs — Cross Axis
MDN Web Docs — calc
MDN Web Docs — perspective
MDN Web Docs — transform-style
MDN Web Docs — backface-visibility
MDN Web Docs — Using data attributes
MDN Web Docs — order
MDN Web Docs — IIFE
MDN Web Docs — ternary operator
MDN Web Docs — destructuring assignment
Originally published at marina-ferreira.github.io.