Reactivity

Declare state

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import Component from "@glimmer/component";

export default class NameComponent extends Component {
  name = "John";

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

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import m from "mithril";

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

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

Update state

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import Component from "@glimmer/component";
import { tracked } from "@glimmer/tracking";

export default class CounterComponent extends Component {
  @tracked name = "John";

  constructor(owner, args) {
    super(owner, args);

    this.name = "Jane";
  }

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

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import m from "mithril";

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

Computed state

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import Component, { tracked } from "@glimmer/component";

export default class DoubleCount extends Component {
  @tracked count = 10;

  get doubleCount() {
    return this.count * 2;
  }

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

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import m from "mithril";

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

Templating

Minimal template

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

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import m from "mithril";

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

Styling

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

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

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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

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const colors = ["red", "green", "blue"];

<template>
  <ul>
    {{#each colors as |color|}}
      <li>{{color}}</li>
    {{/each}}
  </ul>
</template>

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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

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import Component from "@glimmer/component";
import { tracked } from "@glimmer/tracking";

export default class Counter extends Component {
  @tracked count = 0;

  incrementCount = () => this.count++;

  <template>
    <p>Counter: {{this.count}}</p>
    <button {{on "click" this.incrementCount}}>+1</button>
  </template>
}

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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

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import { modifier } from "ember-modifier";

const autofocus = modifier((element) => element.focus());

<template>
  <input {{autofocus}} />
</template>

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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

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import Component from "@glimmer/component";
import { tracked } from "@glimmer/tracking";

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

export default class TrafficLight extends Component {
  @tracked lightIndex = 0;

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

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

  <template>
    <button {{on "click" this.nextLight}}>Next light</button>
    <p>Light is: {{this.light}}</p>
    <p>
      You must
      {{#if (eq this.light "red")}}
        STOP
      {{else if (eq this.light "orange")}}
        SLOW DOWN
      {{else if (eq this.light "green")}}
        GO
      {{/if}}
    </p>
  </template>
}

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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

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const pageTitle = () => document.title;

<template>
  <p>Page title is: {{(pageTitle)}}</p>
</template>

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import m from "mithril";

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

On unmount

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import Component from "@glimmer/component";
import { tracked } from "@glimmer/tracking";
import { registerDestructor } from "@ember/destroyable";

export default class Time extends Component {
  @tracked time = new Date().toLocaleTimeString();

  constructor(owner, args) {
    super(owner, args);

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

    registerDestructor(this, () => clearInterval(timer));
  }

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

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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

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import UserProfile from "./user-profile.gjs";

const favoriteColors = ["green", "blue", "red"];

<template>
  <UserProfile
    @name="John"
    @age={{20}}
    @favouriteColors={{favoriteColors}}
    @isAvailable={{true}}
  />
</template>

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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

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<template>
  <button {{on "click" @onYes}}> YES </button>
  <button {{on "click" @onNo}}> NO </button>
</template>

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

Slot

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import FunnyButton from "./funny-button";

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

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

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

Slot fallback

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import FunnyButton from "./funny-button";

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

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

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

Context

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import UserProfile from "./user-profile";

<template>
    <UserProfile />
</template>

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

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

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

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

Form input

Input text

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import Component from "@glimmer/component";
import { tracked } from "@glimmer/tracking";

export default class InputHello extends Component {
  @tracked text = "Hello World";

  handleInput = (event) => (this.text = event.target.value);

  <template>
    <p>{{this.text}}</p>
    <input value={{this.text}} {{on "input" this.handleInput}} />
  </template>
}

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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

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import Component from "@glimmer/component";
import { tracked } from "@glimmer/tracking";

export default class InputHello extends Component {
  @tracked isAvailable = false;

  handleChange = (event) => (this.isAvailable = event.target.checked);

  <template>
    <input
      id="is-available"
      type="checkbox"
      checked={{this.isAvailable}}
      {{on "change" this.handleChange}}
    />
    <label for="is-available">Is available</label>
  </template>
}

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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

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import Component from "@glimmer/component";
import { tracked } from "@glimmer/tracking";

export default class PickPill extends Component {
  @tracked picked = "red";

  handleChange = (event) => (this.picked = event.target.value);

  <template>
    <div>Picked: {{this.picked}}</div>

    <input
      id="blue-pill"
      type="radio"
      value="blue"
      checked={{eq this.picked "blue"}}
      {{on "change" this.handleChange}}
    />
    <label htmlFor="blue-pill">Blue pill</label>

    <input
      id="red-pill"
      type="radio"
      value="red"
      checked={{eq this.picked "red"}}
      {{on "change" this.handleChange}}
    />
    <label htmlFor="red-pill">Red pill</label>
  </template>
}

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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

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import Component from "@glimmer/component";
import { tracked } from "@glimmer/tracking";

export default class ColorSelect extends Component {
  @tracked selectedColorId = 2;

  select = (event) => (this.selectedColorId = event.target.value);

  isSelected = (colorId) => this.selectedColorId === colorId;

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

  <template>
    <select {{on "change" this.select}}>
      {{#each this.colors as |color|}}
        <option
          value={{color.id}}
          disabled={{color.isDisabled}}
          selected={{this.isSelected color.id}}
        >
          {{color.text}}
        </option>
      {{/each}}
    </select>
  </template>
}

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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

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<!doctype html>
<html>
  <body>
    <script type="module" src="./index.js"></script>
  </body>
</html>

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

Fetch data

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import Component from "@glimmer/component";
import { tracked } from "@glimmer/tracking";

class State {
  @tracked isLoading = false;
  @tracked error = null;
  @tracked data = null;
}

function fetchUsers() {
  let state = new State();
  
  async function fetchData() {
    try {
      let response = await fetch("https://randomuser.me/api/?results=3");
      let { results: users } = await response.json();
      state.data = users;
      state.error = null;
    } catch (err) {
      state.data = null;
      state.error = err;
    }
    state.isLoading = false;
  }
  
  fetchData();
  return state;
}

export default class App extends Component {
  <template>
    {{#let (this.fetchUsers) as |request|}}
      {{#if request.isLoading}}
        <p>Fetching users...</p>
      {{else if request.error}}
        <p>An error occurred while fetching users</p>
      {{else}}
        <ul>
          {{#each request.data as |user|}}
            <li>
              <img src={{user.picture.thumbnail}} alt="user" />
              <p>{{user.name.first}} {{user.name.last}}</p>
            </li>
          {{/each}}
        </ul>
      {{/if}}
    {{/let}}
  </template>
}

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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}`),
        ),
      );
    },
  };
}