Lit vs Solid.js comparison

Reactivity

Declare state

Lit

name.js

import { LitElement, html } from "lit";
import { customElement, state } from "lit/decorators.js";

@customElement("x-name")
export class XName extends LitElement {
  @state()
  name = "John";

  render() {
    return html`<h1>Hello ${this.name}!</h1>`;
  }
}

Solid.js

Name.jsx

import { createSignal } from "solid-js";

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

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

Update state

Lit

name.js

import { LitElement, html } from "lit";
import { customElement, state } from "lit/decorators.js";

@customElement("x-name")
export class XName extends LitElement {
  @state()
  name = "John";

  constructor() {
    super();
    this.name = "Jane";
  }

  render() {
    return html`<h1>Hello ${this.name}!</h1>`;
  }
}

Solid.js

Name.jsx

import { createSignal } from "solid-js";

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

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

Computed state

Lit

double-count.js

import { LitElement, html } from "lit";
import { customElement, state } from "lit/decorators.js";

@customElement("double-count")
export class DoubleCount extends LitElement {
  @state()
  count = 10;

  render() {
    const doubleCount = this.count * 2;
    return html`<div>${doubleCount}</div>`;
  }
}

Solid.js

DoubleCount.jsx

import { createSignal } from "solid-js";

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

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

Templating

Minimal template

Lit

hello-world.js

import { LitElement, html } from "lit";
import { customElement } from "lit/decorators.js";

@customElement("hello-world")
export class HelloWorld extends LitElement {
  render() {
    return html`<h1>Hello world</h1>`;
  }
}

Solid.js

HelloWorld.jsx

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

Styling

Lit

css-style.js

import { LitElement, html, css } from "lit";
import { customElement } from "lit/decorators.js";
import { styleMap } from "lit/directives/style-map.js";

@customElement("css-style")
export class CssStyle extends LitElement {
  static styles = css`
    .title {
      color: red;
    }
  `;

  render() {
    return html`
      <h1 class="title">I am red</h1>
      <button style=${styleMap({ fontSize: "10rem" })}>I am a button</button>
    `;
  }
}

Solid.js

CssStyle.jsx

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>
    </>
  );
}

style.css

.title {
  color: red;
}

Loop

Lit

colors-list.js

import { LitElement, html } from "lit";
import { customElement } from "lit/decorators.js";
import { repeat } from "lit/directives/repeat.js";

@customElement("colors-list")
export class ColorsList extends LitElement {
  colors = ["red", "green", "blue"];

  render() {
    return html`
      <ul>
        ${repeat(
          this.colors,
          (color) => color,
          (color) => html`<li>${color}</li>`
        )}
      </ul>
    `;
  }
}

Solid.js

Colors.jsx

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>
  );
}

Event click

Lit

x-counter.js

import { LitElement, html } from "lit";
import { customElement, state } from "lit/decorators.js";

@customElement("x-counter")
export class XCounter extends LitElement {
  @state()
  count = 0;

  incrementCount() {
    this.count = this.count + 1;
  }

  render() {
    return html`
      <p>Counter: ${this.count}</p>
      <button @click=${this.incrementCount}>+1</button>
    `;
  }
}

Solid.js

Counter.jsx

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>
    </>
  );
}

Dom ref

Lit

input-focused.js

import { LitElement, html } from "lit";
import { customElement, state, query } from "lit/decorators.js";

@customElement("input-focused")
export class InputFocused extends LitElement {
  @query("input") inputEl;

  firstUpdated() {
    this.inputEl.focus();
  }

  render() {
    return html`<input type="text" />`;
  }
}

Solid.js

InputFocused.jsx

import { onMount } from "solid-js";

export default function InputFocused() {
  let inputElement;

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

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

Conditional

Lit

traffic-light.js

import { LitElement, html } from "lit";
import { customElement, state } from "lit/decorators.js";
import { choose } from "lit/directives/choose.js";

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

@customElement("traffic-light")
export class TrafficLight extends LitElement {
  @state()
  lightIndex = 0;

  get light() {
    return TRAFFIC_LIGHTS[this.lightIndex];
  }

  nextLight() {
    this.lightIndex = (this.lightIndex + 1) % TRAFFIC_LIGHTS.length;
  }

  render() {
    return html`
      <button @click=${this.nextLight}>Next light</button>
      <p>Light is ${this.light}</p>
      <p>
        You must ${choose(this.light, [
          ["red", () => html`<span>STOP</span>`],
          ["orange", () => html`<span>SLOW DOWN</span>`],
          ["green", () => html`<span>GO</span>`],
        ])}
      </p>
    `;
  }
}

Solid.js

TrafficLight.jsx

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>
    </>
  );
}

Lifecycle

On mount

Lit

page-title.js

import { LitElement, html } from "lit";
import { customElement, state } from "lit/decorators.js";

@customElement("page-title")
export class PageTitle extends LitElement {
  @state()
  pageTitle = "";

  connectedCallback() {
    super.connectedCallback();
    this.pageTitle = document.title;
  }

  render() {
    return html`<p>Page title: ${this.pageTitle}</p>`;
  }
}

Solid.js

PageTitle.jsx

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

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

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

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

On unmount

Lit

x-time.js

import { LitElement, html } from "lit";
import { customElement, state } from "lit/decorators.js";

@customElement("x-time")
export class XTime extends LitElement {
  @state()
  time = "";

  timer;

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

  disconnectedCallback() {
    super.disconnectedCallback();
    clearInterval(this.timer);
  }

  render() {
    return html`<p>Current time: ${this.time}</p>`;
  }
}

Solid.js

Time.jsx

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>;
}

Component composition

Props

Lit

x-app.js

import { LitElement, html } from "lit";
import { customElement } from "lit/decorators.js";

import "./user-profile";

@customElement("x-app")
export class XApp extends LitElement {
  render() {
    return html`<user-profile
      name="John"
      age="20"
      .favouriteColors=${["green", "blue", "red"]}
      isAvailable
    ></user-profile>`;
  }
}

Solid.js

App.jsx

import UserProfile from "./UserProfile.jsx";

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

Emit to parent

Lit

x-app.js

import { LitElement, html } from "lit";
import { customElement, state } from "lit/decorators.js";

import "./answer-button";

@customElement("x-app")
export class XApp extends LitElement {
  @state()
  isHappy = true;

  onAnswerNo() {
    this.isHappy = false;
  }

  onAnswerYes() {
    this.isHappy = true;
  }

  render() {
    return html`
      <p>Are you happy?</p>
      <answer-button
        @yes=${this.onAnswerYes}
        @no=${this.onAnswerNo}
      ></answer-button>
      <p style="font-size: 50px;">${this.isHappy ? "😀" : "😥"}</p>
    `;
  }
}

Solid.js

App.jsx

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>
    </>
  );
}

Slot

Lit

x-app.js

import { LitElement, html } from "lit";
import { customElement } from "lit/decorators.js";

import "./funny-button";

@customElement("x-app")
export class XApp extends LitElement {
  render() {
    return html`<funny-button>Click me!</funny-button>`;
  }
}

Solid.js

App.jsx

import FunnyButton from "./FunnyButton.jsx";

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

Slot fallback

Lit

x-app.js

import { LitElement, html } from "lit";
import { customElement } from "lit/decorators.js";

import "./funny-button";

@customElement("x-app")
export class XApp extends LitElement {
  render() {
    return html`
      <funny-button></funny-button>
      <funny-button>Click me!</funny-button>
    `;
  }
}

Solid.js

App.jsx

import FunnyButton from "./FunnyButton.jsx";

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

Context

Lit

app-x.js

import { LitElement, html } from "lit";
import { customElement, state } from "lit/decorators.js";
import { ContextProvider } from "@lit/context";

import { userContext } from "./user-context";

import "./user-profile";

@customElement("x-app")
export class XApp extends LitElement {
  @state()
  user = {
    id: 1,
    username: "unicorn42",
    email: "unicorn42@example.com",
  };

  provider = new ContextProvider(this, {
    context: userContext,
    initialValue: this.user,
  });

  updateUsername(newUsername) {
    this.user = { ...this.user, username: newUsername };
    this.provider.setValue(this.user);
  }

  render() {
    return html` <h1>Welcome back, ${this.user.username}</h1>
      <user-profile
        .user="${this.user}"
        .updateUsername=${this.updateUsername.bind(this)}
      ></user-profile>`;
  }
}

Solid.js

App.jsx

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: "unicorn42@example.com",
  });

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

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

Form input

Input text

Lit

input-hello.js

import { LitElement, html } from "lit";
import { customElement, state } from "lit/decorators.js";

@customElement("input-hello")
export class InputHello extends LitElement {
  @state()
  text = "Hello World";

  handleInput(event) {
    this.text = event.target.value;
  }

  render() {
    return html`
      <p>${this.text}</p>
      <input value=${this.text} @input=${this.handleInput} />
    `;
  }
}

Solid.js

InputHello.jsx

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} />
    </>
  );
}

Checkbox

Lit

is-available.js

import { LitElement, html } from "lit";
import { customElement, state } from "lit/decorators.js";

@customElement("is-available")
export class IsAvailable extends LitElement {
  @state()
  isAvailable = false;

  handleChange() {
    this.isAvailable = !this.isAvailable;
  }

  render() {
    return html`
      <input
        id="is-available"
        type="checkbox"
        ?checked=${this.isAvailable}
        @change=${this.handleChange}
      />
      <label for="is-available">Is available</label>
    `;
  }
}

Solid.js

IsAvailable.jsx

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>
    </>
  );
}

Radio

Lit

pick-pill.js

import { LitElement, html } from "lit";
import { customElement, state } from "lit/decorators.js";

@customElement("pick-pill")
export class PickPill extends LitElement {
  @state()
  picked = "red";

  handleChange(event) {
    this.picked = event.target.value;
  }

  render() {
    return html`
      <div>Picked: ${this.picked}</div>

      <input
        id="blue-pill"
        name="pill"
        ?checked=${this.picked === "blue"}
        type="radio"
        value="blue"
        @change=${this.handleChange}
      />
      <label for="blue-pill">Blue pill</label>

      <input
        id="red-pill"
        name="pill"
        ?checked=${this.picked === "red"}
        type="radio"
        value="red"
        @change=${this.handleChange}
      />
      <label for="red-pill">Red pill</label>
    `;
  }
}

Solid.js

PickPill.jsx

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>
    </>
  );
}

Select

Lit

color-select.js

import { LitElement, html } from "lit";
import { customElement, state } from "lit/decorators.js";
import { repeat } from "lit/directives/repeat";

@customElement("color-select")
export class ColorSelect extends LitElement {
  colors = [
    { id: 1, text: "red" },
    { id: 2, text: "blue" },
    { id: 3, text: "green" },
    { id: 4, text: "gray", isDisabled: true },
  ];

  @state()
  selectedColorId = 2;

  handleChange(event) {
    this.selectedColorId = event.target.value;
  }

  render() {
    return html`
      <select @change=${this.handleChange}>
        ${repeat(
          this.colors,
          (color) => color.id,
          (color) =>
            html`<option
              value=${color.id}
              ?selected=${this.selectedColorId === color.id}
              ?disabled=${color.isDisabled}
            >
              ${color.text}
            </option>`
        )}
      </select>
    `;
  }
}

Solid.js

ColorSelect.jsx

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>
  );
}

Webapp features

Render app

Lit

index.html

<!DOCTYPE html>
<html>
  <head>
    <script type="module" src="./app.js"></script>
  </head>

  <body>
    <x-app />
  </body>
</html>

Solid.js

index.html

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

Fetch data

Lit

x-app.js

import { LitElement, html } from "lit";
import { customElement } from "lit/decorators.js";
import { createFetchUsersTask } from "./fetch-users-task";

@customElement("x-app")
export class XApp extends LitElement {
  fetchUsers = createFetchUsersTask(this);

  render() {
    return this.fetchUsers.render({
      pending: () => html`<p>Fetching users...</p>`,
      error: (e) => html`<p>An error occurred while fetching users</p>`,
      complete: (data) => html`
        <ul>
          ${data.map(
            (user) => html`
              <li>
                <img src=${user.picture.thumbnail} alt="user" />
                <p>${user.name.first} ${user.name.last}</p>
              </li>
            `
          )}
        </ul>
      `,
    });
  }
}

Solid.js

App.jsx

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>
  );
}

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