Intro to Svelte
Why yet another framework to learn? 🤦♂️🤦♀️
If you are worried about tons of front-end frameworks and their variations out there, why yet another framework?
The frameworks like Angular, ReactJS or VueJS make it easier, faster to spin up applications. More robust and efficient application development within a team.
They changed the way in which we design, develop, and deliver the applications.
More and more frameworks refine the frameworks and make it, even more, easier to develop simple, fast, and efficient applications.
Angular ❤️
Angular is a complete suite but it is bloated.
React 💙
React is a view only
library and uses virtual DOM
but React gets complicated.
Vue 💚
VueJS is a simple to write and has the best parts of React and Angular.
Svelte 🧡
Svelte is a new approach to build user interfaces. The Svelte has no virtual DOM.
Svelte makes you write less code and uses the platform
.
Svelte has no virtual DOM and uses the platform
.
Svelte optimizes the application during the build process that increases your application's performance.
Get the app and start running
Enough of (boring) framework introductions, let us start coding.
Where to start?
"Hello World"
npx degit sveltejs/template hello-world
cd hello-world
You have cloned a template from the sveltejs/template
. Now install the dependencies and spin the server using
npm i
npm run dev
You should see a simple Hello World
application running on localhost:5000.
Let us dive deeper and look at what is generated.
The Svelte
components are defined in .svelte
files. The generated application has the App.svelte
.
The Svelte
components are nothing but a simple HTML
file. All Svelte components can have the following three segments:
- Script - to define the JavaScript
- Style - to define the CSS
- plain HTML - just your HTML and Svelte elements
If you have worked with any frameworks listed above then you might know what are props
.
Props
are attributes that you pass it along theComponents
.
The export let name
inside the script
tag says that the name
is exported from the component and we can send it the information via the attributes.
The props
attached to your components will be first exported
out of the component.
<script>
export let name
</script>
<style>
h1 {
color: purple;
}
</style>
Any variable (including the props) that we defined inside the <script>
component can be used in the HTML component
with {variable_name}
notation. The {}
is used to define the value defined in the script
tag.
<h1>Hello {name}!</h1>
The application starts in the main.js
. We import the App.svelte
(where the App
component is defined).
import App from './App.svelte'
Then we create an App object from the imported App
component. Then we define target
and also pass in props
to the component's constructor.
The target
defines where to render the component in the HTML document.
The props
is the place where we will define the attributes.
const app = new App({
target: document.body,
props: {
name: 'world',
},
})
Finally, export the app
from the main.js
.
export default app
There is the rollup.config.js
which takes care of bundling and building the application.
import App from './App.svelte'
Want a shorter alternative, fork this codesandbox
Tic Tac Toe
Let us re-create the classic Tic Tac Toe
from the react (official) example with Svelte
.
Create a components folder, this is where we will define all the Svelte
components except the App.svelte
.
We will need the following components:
Square.svelte
- Each square in the Tic Tac Toe will be a separatesvelte
component.Board.svelte
- The Board component will hold all the square components. This component will be responsible for passing the data to its childsquare
components and also decide whether the game is still on or finished.Game.svelte
- The Game component is an overall wrapper around theBoard
component.
Let us first create Game.svelte
component. The Game Component will hold the Board
component.
<div class="game">
<Board />
</div>
Now we will need to import the Board
component.
<script>
import Board from './Board.svelte'
</script>
Let us style the board a little bit.
<style>
.game {
display: flex;
flex-direction: row;
}
</style>
The Board component will have three rows of three squares in each.
<div class="board-row">
<Square />
<Square />
<Square />
</div>
<div class="board-row">
<Square />
<Square />
<Square />
</div>
<div class="board-row">
<Square />
<Square />
<Square />
</div>
We will need to import the Square
component in the <script>
section.
<script>
import Square from './Square.svelte'
</script>
Let us style them a little bit.
<style>
.board-row:after {
clear: both;
content: '';
display: table;
}
</style>
Then we will define the Square
component inside the Square.svelte
.
<style>
.square {
background: #fff;
border: 1px solid #999;
float: left;
font-size: 24px;
font-weight: bold;
line-height: 34px;
height: 34px;
margin-right: -1px;
margin-top: -1px;
padding: 0;
text-align: center;
width: 34px;
}
.square:focus {
outline: none;
}
.square:focus {
background: #ddd;
}
</style>
<script>
let value = ''
</script>
<button class="square">{value}</button>
We defined value
and used that inside the button
element.
When we click the button it should change the value into X
. We will use the on:click
event handler.
<button class="square" on:click={() => handleClick}> {value} </button>
The event handler in Svelte
is defined on:<event>
.
Let us define the handleClick
inside the <script>
tag.
function handleClick() {
value = 'X'
}
Now click on the button, you should see the value of button is changed into X
.
There is no
this
, no complex bindings but a simple variable declaration and changing it.
It is not easy to maintain the state in the child component and then propagating it to the parent. Rather we can move the state to the parent and then make the parent decide on how to maintain the child component. To do this, let us change the Board
component and send the value
and the on:click
event handler through the Board
component.
Let us consider both the on:click
and value
is a prop
to the Square
component.
<script>
export let value
export let handleClick
</script>
<button class="square" on:click="{handleClick}">{value}</button>
Now we will modify the Board
component. Instead of defining each Board
we will define an array squares
and use it.
<script>
let squares = Array(9).fill('')
</script>
and change the HTML into
<div class="board-row">
<Square value={squares[0]} handleClick={() => handleClick(0)}/> <Square
value={squares[1]} handleClick={() => handleClick(1)}/> <Square
value={squares[2]} handleClick={() => handleClick(2)}/>
</div>
<div class="board-row">
<Square value={squares[3]} handleClick={() => handleClick(3)} /> <Square
value={squares[4]} handleClick={() => handleClick(4)} /> <Square
value={squares[5]} handleClick={() => handleClick(5)} />
</div>
<div class="board-row">
<Square value={squares[6]} handleClick={() => handleClick(6)} /> <Square
value={squares[7]} handleClick={() => handleClick(7)} /> <Square
value={squares[8]} handleClick={() => handleClick(8)} />
</div>
We will also need to define the handleClick
method.
function handleClick(i) {
squares[i] = 'X'
}
:clap: Congrats that is awesome. Let us build the real game.
The Game is played alternatively, that is one player marks with X
and the other with O
. Let us add that condition in the Board
component.
<!-- Board.svelte -->
let isXTurn = true; function handleClick(i) { squares[i] = isXTurn ? 'X' : 'O';
isXTurn = !isXTurn; }
Cool, now we have to calculate the winner.
function calculateWinner(squares) {
const lines = [
[0, 1, 2],
[3, 4, 5],
[6, 7, 8],
[0, 3, 6],
[1, 4, 7],
[2, 5, 8],
[0, 4, 8],
[2, 4, 6],
]
for (let i = 0; i < lines.length; i++) {
const [a, b, c] = lines[i]
if (squares[a] && squares[a] === squares[b] && squares[a] === squares[c]) {
return squares[a]
}
}
return null
}
The above function will return X
or O
if there is a winner or else just returns a null
.
We will have to check this every time when the user clicks the square. Also once a player clicks a square we should not allow any other clicks on that square.
function handleClick(i) {
if (calculateWinner(squares) || squares[i] !== '') {
return
}
squares[i] = isXTurn ? 'X' : 'O'
isXTurn = !isXTurn
}
We will need to show the game status for the players. The game status information is dynamic. That is it will change and there should be someone listen to it and change the view once updated.
In React world we will have the state
. In Svelte we bind the components with $
. The values will be updated.
$: winner = calculateWinner(squares)
$: status = winner
? 'Winner: ' + winner
: 'Next player:' + (xIsNext ? 'X' : 'O')
We will use the status inside the HTML
.
<div class="status">{status}</div>
<style>
.status {
margin-bottom: 10px;
}
</style>
Now the status is re-computed whenever there is a change.
The Svelte components are slim, no extra boilerplates, no this
and it is much closer to the platform. In fact, they are nothing but simple HTML
.
Check out Svelte example sites for even more awesome demos.
Check out more in the docs here.
We will continue with even more in-depth tutorial about Svelte
.