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Component Party

Reactivity

Declare state

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

<h1>Hello {name}</h1>

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<script>
export default {
  data() {
    return {
      name: "John",
    };
  },
};
</script>

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

Update state

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

<h1>Hello {name}</h1>

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<script>
export default {
  data() {
    return {
      name: "John",
    };
  },
  created() {
    this.name = "Jane";
  },
};
</script>

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

Computed state

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

<div>{doubleCount}</div>

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<script>
export default {
  data() {
    return {
      count: 10,
    };
  },
  computed: {
    doubleCount() {
      return this.count * 2;
    },
  },
};
</script>

<template>
  <div>{{ doubleCount }}</div>
</template>

Templating

Minimal template

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<h1>Hello world</h1>

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<template>
  <h1>Hello world</h1>
</template>

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>

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

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

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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<script>
export default {
  data() {
    return {
      colors: ["red", "green", "blue"],
    };
  },
};
</script>

<template>
  <ul>
    <li v-for="color in colors" :key="color">
      {{ color }}
    </li>
  </ul>
</template>

Event click

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<script>
  let count = 0;

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

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

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<script>
export default {
  data() {
    return {
      count: 0,
    };
  },
  methods: {
    incrementCount() {
      this.count++;
    },
  },
};
</script>

<template>
  <div>
    <p>Counter: {{ count }}</p>
    <button @click="incrementCount">+1</button>
  </div>
</template>

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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<script>
export default {
  mounted() {
    this.$refs.inputElement.focus();
  },
};
</script>

<template>
  <input ref="inputElement" />
</template>

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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<script>
export default {
  data() {
    return {
      TRAFFIC_LIGHTS: ["red", "orange", "green"],
      lightIndex: 0,
    };
  },
  computed: {
    light() {
      return this.TRAFFIC_LIGHTS[this.lightIndex];
    },
  },
  methods: {
    nextLight() {
      this.lightIndex = (this.lightIndex + 1) % this.TRAFFIC_LIGHTS.length;
    },
  },
};
</script>

<template>
  <div>
    <button @click="nextLight">Next light</button>
    <p>Light is: {{ light }}</p>
    <p>
      You must
      <span v-if="light === 'red'">STOP</span>
      <span v-else-if="light === 'orange'">SLOW DOWN</span>
      <span v-else-if="light === 'green'">GO</span>
    </p>
  </div>
</template>

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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<script>
export default {
  data() {
    return {
      pageTitle: "",
    };
  },
  mounted() {
    this.pageTitle = document.title;
  },
};
</script>

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

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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<script>
export default {
  data() {
    return {
      time: new Date().toLocaleTimeString(),
      timer: null,
    };
  },
  mounted() {
    this.timer = setInterval(() => {
      this.time = new Date().toLocaleTimeString();
    }, 1000);
  },
  beforeDestroy() {
    clearInterval(this.timer);
  },
};
</script>

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

Component composition

Props

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

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

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

export default {
  components: {
    UserProfile,
  },
};
</script>

<template>
  <UserProfile
    name="John"
    :age="20"
    :favorite-colors="['green', 'blue', 'red']"
    is-available
  />
</template>

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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<script>
import AnswerButton from "./AnswerButton.vue";
export default {
  components: {
    AnswerButton,
  },
  data() {
    return {
      isHappy: true,
    };
  },
  methods: {
    onAnswerNo() {
      this.isHappy = false;
    },
    onAnswerYes() {
      this.isHappy = true;
    },
  },
};
</script>

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

Slot

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

<FunnyButton>Click me!</FunnyButton>

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<script>
import FunnyButton from "./FunnyButton.vue";
export default {
  components: {
    FunnyButton,
  },
};
</script>

<template>
  <FunnyButton> Click me! </FunnyButton>
</template>

Slot fallback

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

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

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<script>
import FunnyButton from "./FunnyButton.vue";
export default {
  components: {
    FunnyButton,
  },
};
</script>

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

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

export default {
  components: { UserProfile },
  provide() {
    return {
      user: Object.assign(this.user, {
        updateUsername: this.updateUsername,
      }),
    };
  },
  data() {
    return {
      user: {
        id: 1,
        username: "unicorn42",
        email: "[email protected]",
      },
    };
  },
  methods: {
    updateUsername(newUsername) {
      this.user.username = newUsername;
    },
  },
};
</script>

<template>
  <div>
    <h1>Welcome back, {{ user.username }}</h1>
    <UserProfile />
  </div>
</template>

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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<script>
export default {
  data() {
    return {
      text: "Hello World",
    };
  },
};
</script>

<template>
  <div>
    <p>{{ text }}</p>
    <input v-model="text" />
  </div>
</template>

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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<script>
export default {
  data() {
    return {
      isAvailable: true,
    };
  },
};
</script>

<template>
  <div>
    <input id="is-available" v-model="isAvailable" type="checkbox" />
    <label for="is-available">Is available</label>
  </div>
</template>

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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<script>
export default {
  data() {
    return {
      picked: "red",
    };
  },
};
</script>

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

    <input id="blue-pill" v-model="picked" type="radio" value="blue" />
    <label for="blue-pill">Blue pill</label>

    <input id="red-pill" v-model="picked" type="radio" value="red" />
    <label for="red-pill">Red pill</label>
  </div>
</template>

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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<script>
export default {
  data() {
    return {
      selectedColorId: 2,
      colors: [
        { id: 1, text: "red" },
        { id: 2, text: "blue" },
        { id: 3, text: "green" },
        { id: 4, text: "gray", isDisabled: true },
      ],
    };
  },
};
</script>

<template>
  <select v-model="selectedColorId">
    <option
      v-for="color in colors"
      :key="color.id"
      :value="color.id"
      :disabled="color.isDisabled"
    >
      {{ color.text }}
    </option>
  </select>
</template>

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>

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

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<script>
export default {
  data() {
    return {
      isLoading: false,
      error: undefined,
      users: undefined,
    };
  },
  mounted() {
    this.fetchData();
  },
  methods: {
    async fetchData() {
      this.isLoading = true;
      try {
        const response = await fetch("https://randomuser.me/api/?results=3");
        const { results: users } = await response.json();
        this.users = users;
        this.error = undefined;
      } catch (error) {
        this.error = error;
      } finally {
        this.users = undefined;
        this.isLoading = false;
      }
    },
  },
};
</script>

<template>
  <p v-if="isLoading">Fetching users...</p>
  <p v-else-if="error">An error ocurred while fetching users</p>
  <ul v-else-if="users">
    <li v-for="user in users" :key="user.login.uuid">
      <img :src="user.picture.thumbnail" alt="user" />
      <p>
        {{ user.name.first }}
        {{ user.name.last }}
      </p>
    </li>
  </ul>
</template>