Reactivity
Declare state
Update state
Templating
Styling
Loop
Event click
Dom ref
Conditional
<script>
const TRAFFIC_LIGHTS = ["red", "orange", "green"];
let lightIndex = $state(0);
const light = $derived(TRAFFIC_LIGHTS[lightIndex]);
function nextLight() {
lightIndex = (lightIndex + 1) % TRAFFIC_LIGHTS.length;
}
</script>
<button onclick={nextLight}>Next light</button>
<p>Light is: {light}</p>
<p>
You must
{#if light === "red"}
<span>STOP</span>
{:else if light === "orange"}
<span>SLOW DOWN</span>
{:else if light === "green"}
<span>GO</span>
{/if}
</p>
Ember Octane
<button {{on "click" this.nextLight}}>Next light</button>
<p>Light is: {{this.light}}</p>
<p>
You must
{{#if (eq this.light "red")}}
STOP
{{else if (eq this.light "orange")}}
SLOW DOWN
{{else if (eq this.light "green")}}
GO
{{/if}}
</p>Lifecycle
On mount
On unmount
Component composition
Props
Emit to parent
<script>
import AnswerButton from "./AnswerButton.svelte";
let isHappy = $state(true);
function onAnswerNo() {
isHappy = false;
}
function onAnswerYes() {
isHappy = true;
}
</script>
<p>Are you happy?</p>
<AnswerButton onYes={onAnswerYes} onNo={onAnswerNo} />
<p style="font-size: 50px;">{isHappy ? "😀" : "😥"}</p>
Ember Octane
<p>Are you happy?</p>
<AnswerButton @onYes={{this.handleYes}} @onNo={{this.handleNo}} />
<p style="font-size: 50px;">{{if this.isHappy "😀" "😥"}}</p>Slot
Slot fallback
Context
<script>
import { setContext } from "svelte";
import UserProfile from "./UserProfile.svelte";
import createUserState from "./createUserState.svelte.js";
const user = createUserState({
id: 1,
username: "unicorn42",
email: "[email protected]",
});
setContext("user", user);
</script>
<h1>Welcome back, {user.username}</h1>
<UserProfile />
Ember Octane
<UserProfile />Form input
Input text
Checkbox
<script>
let isAvailable = $state(false);
</script>
<input id="is-available" type="checkbox" bind:checked={isAvailable} />
<label for="is-available">Is available</label>
Ember Octane
<input
id="is-available"
type="checkbox"
checked={{this.isAvailable}}
{{on "change" this.handleChange}}
/>
<label for="is-available">Is available</label>Radio
<script>
let picked = $state("red");
</script>
<div>Picked: {picked}</div>
<input id="blue-pill" bind:group={picked} type="radio" value="blue" />
<label for="blue-pill">Blue pill</label>
<input id="red-pill" bind:group={picked} type="radio" value="red" />
<label for="red-pill">Red pill</label>
Ember Octane
<div>Picked: {{this.picked}}</div>
<input
id="blue-pill"
type="radio"
value="blue"
checked={{eq this.picked "blue"}}
{{on "change" this.handleChange}}
/>
<label htmlFor="blue-pill">Blue pill</label>
<input
id="red-pill"
type="radio"
value="red"
checked={{eq this.picked "red"}}
{{on "change" this.handleChange}}
/>
<label htmlFor="red-pill">Red pill</label>Select
<script>
let selectedColorId = $state(2);
const colors = [
{ id: 1, text: "red" },
{ id: 2, text: "blue" },
{ id: 3, text: "green" },
{ id: 4, text: "gray", isDisabled: true },
];
</script>
<select bind:value={selectedColorId}>
{#each colors as color}
<option value={color.id} disabled={color.isDisabled}>
{color.text}
</option>
{/each}
</select>
Ember Octane
<select {{on "change" this.select}}>
{{#each this.colors as |color|}}
<option
value={{color.id}}
disabled={{color.isDisabled}}
selected={{eq color.id this.selectedColorId}}
>
{{color.text}}
</option>
{{/each}}
</select>Webapp features
Render app
Svelte 5
<!doctype html>
<html>
<body>
<div id="app"></div>
<script type="module" src="./app.js"></script>
</body>
</html>
Ember Octane
Missing snippet Help us to improve Component Party 
Fetch data
<script>
import useFetchUsers from "./useFetchUsers.svelte.js";
const response = useFetchUsers();
</script>
{#if response.isLoading}
<p>Fetching users...</p>
{:else if response.error}
<p>An error occurred while fetching users</p>
{:else if response.users}
<ul>
{#each response.users as user}
<li>
<img src={user.picture.thumbnail} alt="user" />
<p>
{user.name.first}
{user.name.last}
</p>
</li>
{/each}
</ul>
{/if}
Ember Octane
{{#let (this.fetchUsers) as |request|}}
{{#if request.isLoading}}
<p>Fetching users...</p>
{{else if request.error}}
<p>An error occurred while fetching users</p>
{{else}}
<ul>
{{#each request.users as |user|}}
<li>
<img src={{user.picture.thumbnail}} alt="user" />
<p>{{user.name.first}} {{user.name.last}}</p>
</li>
{{/each}}
</ul>
{{/if}}
{{/let}}