Lit vs Qwik 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>`;
  }
}

Qwik

Name.tsx

import { component$, useSignal } from "@builder.io/qwik";

export const Name = component$(() => {
  const name = useSignal("John");

  return <h1>Hello {name.value}</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>`;
  }
}

Qwik

Name.tsx

import { component$, useTask$, useSignal } from "@builder.io/qwik";

export const Name = component$(() => {
  const name = useSignal("John");

  useTask$(() => {
    name.value = "Jane";
  });

  return <h1>Hello {name.value}</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>`;
  }
}

Qwik

DoubleCount.tsx

import { component$, useSignal, useComputed$ } from "@builder.io/qwik";

export const DoubleCount = component$(() => {
  const count = useSignal(10);
  const doubleCount = useComputed$(() => count.value * 2);

  return <div>{doubleCount.value}</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>`;
  }
}

Qwik

HelloWorld.tsx

export const HelloWorld = () => {
  return <div>Hello World</div>;
};

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>
    `;
  }
}

Qwik

CssStyle.tsx

import { component$, useStyles$ } from "@builder.io/qwik";

export const App = component$(() => {
  useStyles$(`
    .title {
      color: red;
    }
    `);

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

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>
    `;
  }
}

Qwik

Colors.tsx

import { component$ } from "@builder.io/qwik";

export const Colors = component$(() => {
  const colors = ["red", "green", "blue"];
  return (
    <ul>
      {colors.map((color) => (
        <li key={color}>{color}</li>
      ))}
    </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>
    `;
  }
}

Qwik

Counter.tsx

import { component$, useSignal, $ } from "@builder.io/qwik";

export const Counter = component$(() => {
  const count = useSignal(0);

  const incrementCount = $(() => {
    count.value++;
  });

  return (
    <>
      <p>Counter: {count.value}</p>
      <button onClick$={incrementCount}>Increment</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" />`;
  }
}

Qwik

InputFocused.tsx

import { component$, useVisibleTask$, useSignal } from "@builder.io/qwik";

export const InputFocused = component$(() => {
  const inputElement = useSignal<HTMLInputElement>();

  useVisibleTask$(({ track }) => {
    const el = track(inputElement);
    el?.focus();
  });

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

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>
    `;
  }
}

Qwik

TrafficLight.tsx

import { $, component$, useComputed$, useSignal } from "@builder.io/qwik";

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

export const TrafficLight = component$(() => {
  const lightIndex = useSignal(0);

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

  const nextLight = $(() => {
    lightIndex.value = (lightIndex.value + 1) % TRAFFIC_LIGHTS.length;
  });

  return (
    <>
      <button onClick$={nextLight}>Next light</button>
      <p>Light is: {light.value}</p>
      <p>
        You must {light.value === "red" && <span>STOP</span>}
        {light.value === "orange" && <span>SLOW DOWN</span>}
        {light.value === "green" && <span>GO</span>}
      </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>`;
  }
}

Qwik

PageTitle.tsx

import { component$, useVisibleTask$, useStore } from "@builder.io/qwik";

export const App = component$(() => {
  const store = useStore({
    pageTitle: "",
  });

  useVisibleTask$(() => {
    store.pageTitle = document.title;
  });

  return <p>Page title: {store.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>`;
  }
}

Qwik

Time.tsx

import { component$, useVisibleTask$, useStore } from "@builder.io/qwik";

export const App = component$(() => {
  const store = useStore({
    time: new Date().toLocaleTimeString(),
  });

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

    cleanup(() => clearInterval(timer));
  });

  return <p>Current time: {store.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>`;
  }
}

Qwik

App.tsx

import { component$ } from "@builder.io/qwik";
import UserProfile from "./UserProfile";

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

export default App;

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>
    `;
  }
}

Qwik

App.tsx

import { $, component$, useStore } from "@builder.io/qwik";
import AnswerButton from "./AnswerButton";

const App = component$(() => {
  const store = useStore({
    isHappy: true,
  });

  const onAnswerNo = $(() => {
    store.isHappy = false;
  });

  const onAnswerYes = $(() => {
    store.isHappy = true;
  });

  return (
    <>
      <p>Are you happy?</p>
      <AnswerButton onYes$={onAnswerYes} onNo$={onAnswerNo} />
      <p style={{ fontSize: 50 }}>{store.isHappy ? "😀" : "😥"}</p>
    </>
  );
});

export default App;

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>`;
  }
}

Qwik

App.tsx

import FunnyButton from "./FunnyButton";

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>
    `;
  }
}

Qwik

App.tsx

import FunnyButton from "./FunnyButton";

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

Qwik

App.tsx

import {
  component$,
  useStore,
  useContextProvider,
  createContext,
  $,
} from "@builder.io/qwik";
import UserProfile from "./UserProfile";

export const UserContext = createContext("user-context");

const App = component$(() => {
  const user = useStore({
    id: 1,
    username: "unicorn42",
    email: "unicorn42@example.com",
  });

  const updateUsername = $((newUsername) => {
    user.username = newUsername;
  });

  useContextProvider(UserContext, { user, updateUsername });

  return (
    <>
      <h1>Welcome back, {user.username}</h1>
      <UserProfile />
    </>
  );
});

export default App;

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} />
    `;
  }
}

Qwik

InputHello.tsx

import { component$, useSignal } from "@builder.io/qwik";

const InputHello = component$(() => {
  const text = useSignal("");

  return (
    <>
      <p>{text.value}</p>
      <input bind:value={text} />
    </>
  );
});

export default InputHello;

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>
    `;
  }
}

Qwik

IsAvailable.tsx

import { component$, useSignal } from "@builder.io/qwik";

const IsAvailable = component$(() => {
  const isAvailable = useSignal(false);

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

export default IsAvailable;

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>
    `;
  }
}

Qwik

PickPill.tsx

import { component$, useSignal } from "@builder.io/qwik";

const PickPill = component$(() => {
  const pickedColor = useSignal("red");

  return (
    <>
      <div>Picked: {pickedColor.value}</div>
      <input
        id="blue-pill"
        type="radio"
        bind:value={pickedColor}
        checked={pickedColor.value === "blue"}
        value="blue"
      />
      <label for="blue-pill">Blue pill</label>

      <input
        id="red-pill"
        type="radio"
        checked={pickedColor.value === "red"}
        bind:value={pickedColor}
        value="red"
      />
      <label for="red-pill">Red pill</label>
    </>
  );
});

export default PickPill;

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>
    `;
  }
}

Qwik

ColorSelect.tsx

import { component$, useSignal } from "@builder.io/qwik";

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

const ColorSelect = component$(() => {
  const selectedColorId = useSignal("2");

  return (
    <select bind:value={selectedColorId}>
      {colors.map((color) => (
        <option
          key={color.id}
          value={color.id}
          disabled={color.isDisabled}
          selected={`${color.id}` === selectedColorId.value}
        >
          {color.text}
        </option>
      ))}
    </select>
  );
});

export default ColorSelect;

Webapp features

Render app

Lit

index.html

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

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

Qwik

index.html

<!DOCTYPE html>
<html>
  <body>
    <div id="app"></div>
    <script type="module" src="./main.tsx"></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>
      `,
    });
  }
}

Qwik

App.tsx

import { component$, useResource$, Resource } from "@builder.io/qwik";

type UsersResponse = {
  results: {
    picture: {
      thumbnail: string;
    };
    name: {
      first: string;
      last: string;
    };
  }[];
};

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

export const App = component$(() => {
  const data = useResource$<UsersResponse>(fetchUsers);

  return (
    <Resource
      value={data}
      onPending={() => <p>Fetching users...</p>}
      onRejected={() => <p>An error occurred while fetching users</p>}
      onResolved={({ results: users }) => (
        <ul>
          {users.map((user) => (
            <li>
              <img src={user.picture.thumbnail} alt="user" />
              <p>
                {user.name.first} {user.name.last}
              </p>
            </li>
          ))}
        </ul>
      )}
    />
  );
});

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