Reactivity

Declare state

Solid.js

import { createSignal } from "solid-js";

export default function Name() {
  const [name] = createSignal("John");

  return <h1>Hello {name()}</h1>;
}

Svelte 4

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

<h1>Hello {name}</h1>

Update state

Solid.js

import { createSignal } from "solid-js";

export default function Name() {
  const [name, setName] = createSignal("John");
  setName("Jane");

  return <h1>Hello {name()}</h1>;
}

Svelte 4

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

<h1>Hello {name}</h1>

Computed state

Solid.js

import { createSignal } from "solid-js";

export default function DoubleCount() {
  const [count] = createSignal(10);
  const doubleCount = () => count() * 2;

  return <div>{doubleCount()}</div>;
}

Svelte 4

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

<div>{doubleCount}</div>

Templating

Minimal template

Solid.js

export default function HelloWorld() {
  return <h1>Hello World!</h1>;
}

Svelte 4

<h1>Hello world</h1>

Styling

Solid.js

import "./style.css";

export default function CssStyle() {
  return (
    <>
      <h1 class="title">I am red</h1>
      <button style={{ "font-size": "10rem" }}>I am a button</button>
    </>
  );
}

Svelte 4

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

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

Loop

Solid.js

import { For } from "solid-js";

export default function Colors() {
  const colors = ["red", "green", "blue"];

  return (
    <ul>
      <For each={colors}>{(color) => <li>{color}</li>}</For>
    </ul>
  );
}

Svelte 4

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

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

Event click

Solid.js

import { createSignal } from "solid-js";

export default function Counter() {
  const [count, setCount] = createSignal(0);

  function incrementCount() {
    setCount(count() + 1);
  }

  return (
    <>
      <p>Counter: {count()}</p>
      <button onClick={incrementCount}>+1</button>
    </>
  );
}

Svelte 4

<script>
  let count = 0;

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

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

Dom ref

Solid.js

import { onMount } from "solid-js";

export default function InputFocused() {
  let inputElement;

  onMount(() => inputElement.focus());

  return <input ref={inputElement} type="text" />;
}

Svelte 4

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

  let inputElement;

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

<input bind:this={inputElement} />

Conditional

Solid.js

import { createSignal, Switch, Match } from "solid-js";

const TRAFFIC_LIGHTS = ["red", "orange", "green"];

export default function TrafficLight() {
  const [lightIndex, setLightIndex] = createSignal(0);

  const light = () => TRAFFIC_LIGHTS[lightIndex()];

  function nextLight() {
    setLightIndex((lightIndex() + 1) % TRAFFIC_LIGHTS.length);
  }

  return (
    <>
      <button onClick={nextLight}>Next light</button>
      <p>Light is: {light()}</p>
      <p>
        You must
        <Switch>
          <Match when={light() === "red"}>
            <span>STOP</span>
          </Match>
          <Match when={light() === "orange"}>
            <span>SLOW DOWN</span>
          </Match>
          <Match when={light() === "green"}>
            <span>GO</span>
          </Match>
        </Switch>
      </p>
    </>
  );
}

Svelte 4

<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

Solid.js

import { createSignal, onMount } from "solid-js";

export default function PageTitle() {
  const [pageTitle, setPageTitle] = createSignal("");

  onMount(() => {
    setPageTitle(document.title);
  });

  return <p>Page title: {pageTitle()}</p>;
}

Svelte 4

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

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

On unmount

Solid.js

import { createSignal, onCleanup } from "solid-js";

export default function Time() {
  const [time, setTime] = createSignal(new Date().toLocaleTimeString());

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

  onCleanup(() => clearInterval(timer));

  return <p>Current time: {time()}</p>;
}

Svelte 4

<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

Solid.js

import UserProfile from "./UserProfile.jsx";

export default function App() {
  return (
    <UserProfile
      name="John"
      age={20}
      favouriteColors={["green", "blue", "red"]}
      isAvailable
    />
  );
}

Svelte 4

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

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

Emit to parent

Solid.js

import { createSignal } from "solid-js";
import AnswerButton from "./AnswerButton.jsx";

export default function App() {
  const [isHappy, setIsHappy] = createSignal(true);

  function onAnswerNo() {
    setIsHappy(false);
  }

  function onAnswerYes() {
    setIsHappy(true);
  }

  return (
    <>
      <p>Are you happy?</p>
      <AnswerButton onYes={onAnswerYes} onNo={onAnswerNo} />
      <p style={{ "font-size": "50px" }}>{isHappy() ? "😀" : "😥"}</p>
    </>
  );
}

Svelte 4

<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

Solid.js

import FunnyButton from "./FunnyButton.jsx";

export default function App() {
  return <FunnyButton>Click me!</FunnyButton>;
}

Svelte 4

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

<FunnyButton>Click me!</FunnyButton>

Slot fallback

Solid.js

import FunnyButton from "./FunnyButton.jsx";

export default function App() {
  return (
    <>
      <FunnyButton />
      <FunnyButton>I got content!</FunnyButton>
    </>
  );
}

Svelte 4

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

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

Context

Solid.js

import { createSignal } from "solid-js";

import { UserContext } from "./UserContext";
import UserProfile from "./UserProfile";

export default function App() {
  const [user, setUser] = createSignal({
    id: 1,
    username: "unicorn42",
    email: "[email protected]",
  });

  function updateUsername(newUsername) {
    setUser({ ...user(), username: newUsername });
  }

  return (
    <>
      <h1>Welcome back, {user().username}</h1>
      <UserContext.Provider value={[user, updateUsername]}>
        <UserProfile />
      </UserContext.Provider>
    </>
  );
}

Svelte 4

<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 />

Form input

Input text

Solid.js

import { createSignal } from "solid-js";

export default function InputHello() {
  const [text, setText] = createSignal("Hello world");

  function handleChange(event) {
    setText(event.target.value);
  }

  return (
    <>
      <p>{text()}</p>
      <input value={text()} onInput={handleChange} />
    </>
  );
}

Svelte 4

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

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

Checkbox

Solid.js

import { createSignal } from "solid-js";

export default function IsAvailable() {
  const [isAvailable, setIsAvailable] = createSignal(false);

  function handleChange() {
    setIsAvailable((previousValue) => !previousValue);
  }

  return (
    <>
      <input
        id="is-available"
        type="checkbox"
        checked={isAvailable()}
        onChange={handleChange}
      />
      <label for="is-available">Is available</label>
    </>
  );
}

Svelte 4

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

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

Radio

Solid.js

import { createSignal } from "solid-js";

export default function PickPill() {
  const [picked, setPicked] = createSignal("red");

  function handleChange(event) {
    setPicked(event.target.value);
  }

  return (
    <>
      <div>Picked: {picked()}</div>
      <input
        id="blue-pill"
        checked={picked() === "blue"}
        type="radio"
        value="blue"
        onChange={handleChange}
      />
      <label for="blue-pill">Blue pill</label>

      <input
        id="red-pill"
        checked={picked() === "red"}
        type="radio"
        value="red"
        onChange={handleChange}
      />
      <label for="red-pill">Red pill</label>
    </>
  );
}

Svelte 4

<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

Solid.js

import { createSignal, For } from "solid-js";

const colors = [
  { id: 1, text: "red" },
  { id: 2, text: "blue" },
  { id: 3, text: "green" },
  { id: 4, text: "gray", isDisabled: true },
];

export default function ColorSelect() {
  const [selectedColorId, setSelectedColorId] = createSignal(2);

  function handleChange(event) {
    setSelectedColorId(event.target.value);
  }

  return (
    <select value={selectedColorId()} onChange={handleChange}>
      <For each={colors}>
        {(color) => (
          <option value={color.id} disabled={color.isDisabled}>
            {color.text}
          </option>
        )}
      </For>
    </select>
  );
}

Svelte 4

<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

Solid.js

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

Svelte 4

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

Fetch data

Solid.js

import { createResource, For, Switch, Match } from "solid-js";

async function fetchUsers() {
  return (await fetch("https://randomuser.me/api/?results=3")).json();
}

export default function App() {
  const [data] = createResource(fetchUsers);
  const users = () => data()?.results;

  return (
    <Switch>
      <Match when={data.loading}>
        <p>Fetching users...</p>
      </Match>
      <Match when={data.error}>
        <p>An error occurred while fetching users</p>
      </Match>
      <Match when={users()}>
        <ul>
          <For each={users()}>
            {(user) => (
              <li>
                <img src={user.picture.thumbnail} alt="user" />
                <p>
                  {user.name.first} {user.name.last}
                </p>
              </li>
            )}
          </For>
        </ul>
      </Match>
    </Switch>
  );
}

Svelte 4

<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}

Reactivity #

Declare state #

Solid.js

Svelte 4

Update state #

Solid.js

Svelte 4

Computed state #

Solid.js

Svelte 4

Templating #

Minimal template #

Solid.js

Svelte 4

Styling #

Solid.js

Svelte 4

Loop #

Solid.js

Svelte 4

Event click #

Solid.js

Svelte 4

Dom ref #

Solid.js

Svelte 4

Conditional #

Solid.js

Svelte 4

Lifecycle #

On mount #

Solid.js

Svelte 4

On unmount #

Solid.js

Svelte 4

Component composition #

Props #

Solid.js

Svelte 4

Emit to parent #

Solid.js

Svelte 4

Slot #

Solid.js

Svelte 4

Slot fallback #

Solid.js

Svelte 4

Context #

Solid.js

Svelte 4

Form input #

Input text #

Solid.js

Svelte 4

Checkbox #

Solid.js

Svelte 4

Radio #

Solid.js

Svelte 4

Select #

Solid.js

Svelte 4

Webapp features #

Render app #

Solid.js

Svelte 4

Fetch data #

Solid.js

Svelte 4

Reactivity

Declare state

Update state

Computed state

Templating

Minimal template

Styling

Loop

Event click

Dom ref

Conditional

Lifecycle

On mount

On unmount

Component composition

Props

Emit to parent

Slot

Slot fallback

Context

Form input

Input text

Checkbox

Radio

Select

Webapp features

Render app

Fetch data