Lit vs Mithril 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>`;
  }
}

Mithril

Name.js

import m from "mithril";

export default function Name() {
  let name = "John";

  return {
    view: () => m("h1", `Hello ${name}`),
  };
}

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>`;
  }
}

Mithril

Name.js

import m from "mithril";

export default function Name() {
  let name = "John";
  name = "Jane";
  return {
    view: () => m("h1", `Hello ${name}`),
  };
}

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>`;
  }
}

Mithril

DoubleCount.js

import m from "mithril";

export default function DoubleCount() {
  let count = 10;
  let doubleCount = count * 2;
  return {
    view: () => m("div", doubleCount),
  };
}

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>`;
  }
}

Mithril

HelloWorld.js

import m from "mithril";

export default function HelloWorld() {
  return {
    view: () => m("h1", "Hello World"),
  };
}

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>
    `;
  }
}

Mithril

CssStyle.js

import "./style.css";
import m from "mithril";

export default function CssStyle() {
  return {
    view: () =>
      m(
        "div",
        m("h1.title", "I am red"),
        m("button", { style: { fontSize: "10rem" } }, "I am a 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>
    `;
  }
}

Mithril

Colors.js

import m from "mithril";

export default function Colors() {
  const colors = ["red", "green", "blue"];
  return {
    view: () =>
      m(
        "ul",
        colors.map((color, idx) => m("li", { key: idx }, color))
      ),
  };
}

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>
    `;
  }
}

Mithril

Counter.js

import m from "mithril";

export default function Counter() {
  let count = 0;
  const incrementCount = () => (count = count + 1);
  return {
    view: () =>
      m(
        "div",
        m("p", `Counter: ${count}`),
        m("button", { onclick: incrementCount }, "+1")
      ),
  };
}

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" />`;
  }
}

Mithril

InputFocused.js

import m from "mithril";

export default function InputFocused() {
  let value = "";
  return {
    view: () =>
      m("input", {
        oncreate: ({ dom }) => dom.focus(),
        type: "text",
        value,
        oninput: (e) => (value = e.target.value),
      }),
  };
}

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>
    `;
  }
}

Mithril

TrafficLight.js

import m from "mithril";
const TRAFFIC_LIGHTS = ["red", "orange", "green"];

export default function TrafficLight() {
  let lightIndex = 0;
  let currentLight = () => TRAFFIC_LIGHTS[lightIndex];

  const nextLight = () => (lightIndex + 1) % TRAFFIC_LIGHTS.length;

  const instructions = () => {
    switch (currentLight()) {
      case "red":
        return "STOP";
      case "orange":
        return "SLOW DOWN";
      case "green":
        return "GO";
    }
  };

  return {
    view: () =>
      m(
        "div",
        m("button", { onclick: nextLight }, "Next light"),
        m("p", `Light is: ${currentLight()}`),
        m("p", "You must ", m("span", instructions()))
      ),
  };
}

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>`;
  }
}

Mithril

PageTitle.js

import m from "mithril";

export default function PageTitle() {
  return {
    view: () => m("p", `Page title: ${document.title}`),
  };
}

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>`;
  }
}

Mithril

Time.js

import m from "mithril";

export default function Time() {
  let time = new Date().toLocaleTimeString();

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

  return {
    view: () => m("p", `Current time: ${time}`),
    onremove: () => clearInterval(timer),
  };
}

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>`;
  }
}

Mithril

App.js

import m from "mithril";
import UserProfile from "./UserProfile.js";

export default function App() {
  return {
    view: () =>
      m(UserProfile, {
        name: "john",
        age: 20,
        favouriteColors: ["green", "blue", "red"],
        isAvailable: true,
      }),
  };
}

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>
    `;
  }
}

Mithril

AnswerButton.js

import m from "mithril";
export const AnswerButton = ({ attrs: { onYes, onNo } }) => ({
  view: () =>
    m(
      "div",
      m("button", { onclick: onYes }, "YES"),
      m("button", { onclick: onNo }, "NO")
    ),
});

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>`;
  }
}

Mithril

App.js

import m from "mithril";
import { FunnyButton } from "./FunnyButton.jsx";

export default function App() {
  return {
    view: () => m(FunnyButton, "Click me!"),
  };
}

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>
    `;
  }
}

Mithril

App.js

import m from "mithril";
import FunnyButton from "./FunnyButton.jsx";

export default function App() {
  return {
    view: () => m("", m(FunnyButton), m(FunnyButton, "I got Content")),
  };
}

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>`;
  }
}

Mithril

App.js

import m from "mithril";
import UserProfile from "./UserProfile";

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

  const updateUsername = (username) => (user.username = username);

  return {
    view: () =>
      m(
        "",
        m("h1", `Welcome Back, ${user.username}`),
        m(UserProfile, { user, updateUsername })
      ),
  };
}

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} />
    `;
  }
}

Mithril

InputHello.js

import m from "mithril";

export default function InputHello() {
  let text = "Hello world";
  const handleChange = ({ target: { value } }) => (text = value);

  return {
    view: () =>
      m("", m("p", text), m("input", { value: text, onchange: 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>
    `;
  }
}

Mithril

IsAvailable.js

import m from "mithril";

export default function IsAvailable() {
  let isAvailable = false;
  const onUpdate = () => (isAvailable = !isAvailable);

  return {
    view: () =>
      m(
        "",

        m("input", {
          id: "is-available",
          type: "checkbox",
          checked: isAvailable,
          onchange: onUpdate,
        }),
        m("label", { for: "is-available" }, "Is available")
      ),
  };
}

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>
    `;
  }
}

Mithril

PickPill.js

import m from "mithril";

export default function PickPill() {
  let picked = "red";
  let pills = ["red", "green", "blue"];
  const handleChange = ({ target: { value } }) => (picked = value);

  return {
    view: () =>
      m(
        "",
        m("", `Picked: ${picked}`),
        pills.map((pill) =>
          m(
            ".",
            m("input", {
              id: pill,
              checked: picked == pill,
              type: "radio",
              value: pill,
              onchange: handleChange,
            }),
            m("label", { for: pill }, pill)
          )
        )
      ),
  };
}

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>
    `;
  }
}

Mithril

ColorSelect.js

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

export default function ColorSelect() {
  let selectedColorId = 2;

  const handleSelect = ({ target: { value } }) => (selectedColorId = value);

  return {
    view: () =>
      m(
        "select",
        { value: selectedColorId, onchange: handleSelect },
        colors.map(({ id, text, isDisabled }) =>
          m("option", { key: id, id, disabled: isDisabled, value: id }, text)
        )
      ),
  };
}

Webapp features

Render app

Lit

index.html

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

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

Mithril

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>
      `,
    });
  }
}

Mithril

App.js

import m from "mithril";

export default function App() {
  let isLoading = false;
  let error = null;
  let users = [];

  async function fetchUsers() {
    isLoading = true;
    try {
      const { results } = await m.request(
        "https://randomuser.me/api/?results=3"
      );
      users = results;
    } catch (err) {
      error = err;
    }
    isLoading = false;
  }

  return {
    oninit: fetchUsers,
    view() {
      if (isLoading) return m("p", "Fetching users...");
      if (error) return m("p", "An error occurred while fetching users");
      return users.map((user) =>
        m(
          "li",
          { key: user.login.uuid },
          m("img", { src: user.picture.thumbnail, alt: "user" }),
          m("p", `${user.name.first} ${user.name.last}`)
        )
      );
    },
  };
}

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