Reactivity

Declare state

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<script>
  let name = "John";
</script>

<h1>Hello {name}</h1>

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<h1>Hello ${name}</h1>

Update state

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<script>
  let name = "John";
  name = "Jane";
</script>

<h1>Hello {name}</h1>

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<h1>Hello ${name}</h1>

Computed state

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<script>
  let count = 10;
  $: doubleCount = count * 2;
</script>

<div>{doubleCount}</div>

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<div>${doubleCount}</div>

Templating

Minimal template

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<h1>Hello world</h1>

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<h1>Hello world</h1>

Styling

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<h1 class="title">I am red</h1>
<button style="font-size: 10rem;">I am a button</button>

<style>
  .title {
    color: red;
  }
</style>

logo of Aurelia 2 Aurelia 2

.title {
  color: red;
}

Loop

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<script>
  const colors = ["red", "green", "blue"];
</script>

<ul>
  {#each colors as color (color)}
    <li>{color}</li>
  {/each}
</ul>

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<ul>
  <li repeat.for="color of colors">${color}</li>
</ul>

Event click

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<script>
  let count = 0;

  function incrementCount() {
    count++;
  }
</script>

<p>Counter: {count}</p>
<button on:click={incrementCount}>+1</button>

logo of Aurelia 2 Aurelia 2

<p>Counter: ${count}</p>
<button click.trigger="incrementCount">+1</button>

Dom ref

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<script>
  import { onMount } from "svelte";

  let inputElement;

  onMount(() => {
    inputElement.focus();
  });
</script>

<input bind:this={inputElement} />

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<input ref="inputElement" />

Conditional

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<script>
  const TRAFFIC_LIGHTS = ["red", "orange", "green"];
  let lightIndex = 0;

  $: light = TRAFFIC_LIGHTS[lightIndex];

  function nextLight() {
    lightIndex = (lightIndex + 1) % TRAFFIC_LIGHTS.length;
  }
</script>

<button on:click={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>

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<button click.trigger="nextLight()">Next light</button>
<p>Light is: ${light}</p>
<p switch.bind="light">
  You must
  <span case="red">STOP</span>
  <span case="orange">SLOW DOWN</span>
  <span case="green">GO</span>
</p>

Lifecycle

On mount

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<script>
  import { onMount } from "svelte";
  let pageTitle = "";
  onMount(() => {
    pageTitle = document.title;
  });
</script>

<p>Page title: {pageTitle}</p>

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<p>Page title is: ${pageTitle}</p>

On unmount

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<script>
  import { onDestroy } from "svelte";

  let time = new Date().toLocaleTimeString();

  const timer = setInterval(() => {
    time = new Date().toLocaleTimeString();
  }, 1000);

  onDestroy(() => clearInterval(timer));
</script>

<p>Current time: {time}</p>

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<p>Current time: ${time}</p>

Component composition

Props

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<script>
  import UserProfile from "./UserProfile.svelte";
</script>

<UserProfile
  name="John"
  age={20}
  favouriteColors={["green", "blue", "red"]}
  isAvailable
/>

logo of Aurelia 2 Aurelia 2

<user-profile
  name.bind
  age.bind
  favourite-colors.bind="colors"
  is-available.bind="available"
></user-profile>

Emit to parent

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<script>
  import AnswerButton from "./AnswerButton.svelte";

  let isHappy = true;

  function onAnswerNo() {
    isHappy = false;
  }

  function onAnswerYes() {
    isHappy = true;
  }
</script>

<p>Are you happy?</p>
<AnswerButton on:yes={onAnswerYes} on:no={onAnswerNo} />
<p style="font-size: 50px;">{isHappy ? "😀" : "😥"}</p>

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<p>Can I come ?</p>
<answer-button action-handler.bind="handleAnswer"></answer-button>
<p style="font-size: 50px">${isHappy ? "😀" : "😥"}</p>

Slot

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<script>
  import FunnyButton from "./FunnyButton.svelte";
</script>

<FunnyButton>Click me!</FunnyButton>

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<funny-button>Click me !</funny-button>

Slot fallback

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<script>
  import FunnyButton from "./FunnyButton.svelte";
</script>

<FunnyButton />
<FunnyButton>I got content!</FunnyButton>

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<funny-button></funny-button>
<funny-button>Click me !</funny-button>

Context

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<script>
  import { setContext } from "svelte";
  import UserProfile from "./UserProfile.svelte";
  import createUserStore from "./createUserStore.js";

  const userStore = createUserStore({
    id: 1,
    username: "unicorn42",
    email: "[email protected]",
  });

  setContext("user", userStore);
</script>

<h1>Welcome back, {$userStore.username}</h1>
<UserProfile />

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<h1>Welcome back, {{ user.username }}</h1>
<user-profile />

Form input

Input text

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<script>
  let text = "Hello World";
</script>

<p>{text}</p>
<input bind:value={text} />

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<p>${text}</p>
<input value.bind />

Checkbox

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<script>
  let isAvailable = false;
</script>

<input id="is-available" type="checkbox" bind:checked={isAvailable} />
<label for="is-available">Is available</label>

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<input id="is-available" type="checkbox" checked.bind="isAvailable" />
<label for="is-available">Is available</label>: ${isAvailable}

Radio

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<script>
  let picked = "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>

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<div>Picked: ${picked}</div>

<input id="blue-pill" checked.bind="picked" type="radio" value="blue" />
<label for="blue-pill">Blue pill</label>

<input id="red-pill" checked.bind="picked" type="radio" value="red" />
<label for="red-pill">Red pill</label>

Select

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<script>
  let selectedColorId = 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>

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<select value.bind="selectedColorId">
  <option value="">Select A Color</option>
  <option
    repeat.for="color of colors"
    value.bind="color.id"
    disabled.bind="color.isDisabled"
  >
    ${color.text}
  </option>
</select>

Webapp features

Render app

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<!doctype html>
<html>
  <body>
    <div id="app"></div>
    <script type="module" src="./app.js"></script>
  </body>
</html>

logo of Aurelia 2 Aurelia 2

<!doctype html>
<html>
  <head>
    <script type="module" src="./main.ts"></script>
  </head>

  <body>
    <app></app>
  </body>
</html>

Fetch data

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<script>
  import useFetchUsers from "./useFetchUsers";

  const { isLoading, error, data: users } = useFetchUsers();
</script>

{#if $isLoading}
  <p>Fetching users...</p>
{:else if $error}
  <p>An error occurred while fetching users</p>
{:else if $users}
  <ul>
    {#each $users as user}
      <li>
        <img src={user.picture.thumbnail} alt="user" />
        <p>
          {user.name.first}
          {user.name.last}
        </p>
      </li>
    {/each}
  </ul>
{/if}

logo of Aurelia 2 Aurelia 2

<template promise.bind="useFetchUsers.fetchData()">
  <p pending>Fetching users...</p>
  <p catch>An error ocurred while fetching users</p>
  <ul then.from-view="users">
    <li repeat.for="user of users">
      <img src.bind="user.picture.thumbnail" alt="user" />
      <p>${ user.name.first } ${ user.name.last }</p>
    </li>
  </ul>
</template>