Vue 3 vs Svelte 4 comparison

Declare state

Vue 3

Name.vue

<script setup>
import { ref } from "vue";
const name = ref("John");
</script>

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

Svelte 4

Name.svelte

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

<h1>Hello {name}</h1>

Update state

Vue 3

Name.vue

<script setup>
import { ref } from "vue";
const name = ref("John");
name.value = "Jane";
</script>

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

Svelte 4

Name.svelte

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

<h1>Hello {name}</h1>

Computed state

Vue 3

DoubleCount.vue

<script setup>
import { ref, computed } from "vue";
const count = ref(10);
const doubleCount = computed(() => count.value * 2);
</script>

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

Svelte 4

DoubleCount.svelte

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

<div>{doubleCount}</div>

Templating

Minimal template

Vue 3

HelloWorld.vue

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

Svelte 4

HelloWorld.svelte

<h1>Hello world</h1>

Styling

Vue 3

CssStyle.vue

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

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

Svelte 4

CssStyle.svelte

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

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

Loop

Vue 3

Colors.vue

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

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

Svelte 4

Colors.svelte

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

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

Event click

Vue 3

Counter.vue

<script setup>
import { ref } from "vue";
const count = ref(0);

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

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

Svelte 4

Counter.svelte

<script>
  let count = 0;

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

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

Dom ref

Vue 3

InputFocused.vue

<script setup>
import { useTemplateRef, onMounted } from "vue";

const inputElement = useTemplateRef("inputElement");

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

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

Svelte 4

InputFocused.svelte

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

  let inputElement;

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

<input bind:this={inputElement} />

Conditional

Vue 3

TrafficLight.vue

<script setup>
import { ref, computed } from "vue";
const TRAFFIC_LIGHTS = ["red", "orange", "green"];
const lightIndex = ref(0);

const light = computed(() => TRAFFIC_LIGHTS[lightIndex.value]);

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

<template>
  <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>
</template>

Svelte 4

TrafficLight.svelte

<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>

Lifecycle

On mount

Vue 3

PageTitle.vue

<script setup>
import { ref, onMounted } from "vue";
const pageTitle = ref("");
onMounted(() => {
  pageTitle.value = document.title;
});
</script>

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

Svelte 4

PageTitle.svelte

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

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

On unmount

Vue 3

Time.vue

<script setup>
import { ref, onUnmounted } from "vue";

const time = ref(new Date().toLocaleTimeString());

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

onUnmounted(() => {
  clearInterval(timer);
});
</script>

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

Svelte 4

Time.svelte

<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>

Component composition

Props

Vue 3

App.vue

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

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

Svelte 4

App.svelte

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

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

Emit to parent

Vue 3

App.vue

<script setup>
import { ref } from "vue";
import AnswerButton from "./AnswerButton.vue";

let isHappy = ref(true);

function onAnswerNo() {
  isHappy.value = false;
}

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

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

Svelte 4

App.svelte

<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>

Slot

Vue 3

App.vue

<script setup>
import FunnyButton from "./FunnyButton.vue";
</script>

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

Svelte 4

App.svelte

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

<FunnyButton>Click me!</FunnyButton>

Slot fallback

Vue 3

App.vue

<script setup>
import FunnyButton from "./FunnyButton.vue";
</script>

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

Svelte 4

App.svelte

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

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

Context

Vue 3

App.vue

<script setup>
import { ref, provide } from "vue";
import UserProfile from "./UserProfile.vue";

const user = ref({
  id: 1,
  username: "unicorn42",
  email: "unicorn42@example.com",
});

function updateUsername(username) {
  user.value.username = username;
}

provide("user", { user, updateUsername });
</script>

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

Svelte 4

App.svelte

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

  const userStore = createUserStore({
    id: 1,
    username: "unicorn42",
    email: "unicorn42@example.com",
  });

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

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

Form input

Input text

Vue 3

InputHello.vue

<script setup>
import { ref } from "vue";
const text = ref("Hello World");
</script>

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

Svelte 4

InputHello.svelte

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

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

Checkbox

Vue 3

IsAvailable.vue

<script setup>
import { ref } from "vue";

const isAvailable = ref(true);
</script>

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

Svelte 4

IsAvailable.svelte

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

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

Radio

Vue 3

PickPill.vue

<script setup>
import { ref } from "vue";

const picked = ref("red");
</script>

<template>
  <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>
</template>

Svelte 4

PickPill.svelte

<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>

Select

Vue 3

ColorSelect.vue

<script setup>
import { ref } from "vue";

const selectedColorId = ref(2);

const 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>

Svelte 4

ColorSelect.svelte

<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>

Webapp features

Render app

Vue 3

index.html

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

Svelte 4

index.html

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

Fetch data

Vue 3

App.vue

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

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

Svelte 4

App.svelte

<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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