Reactivity

Declare state

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import m from "mithril";

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

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

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<template>
  <h1>Hello ${name}</h1>
</template>

Update state

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import m from "mithril";

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

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<template>
  <h1>Hello ${name}</h1>
</template>

Computed state

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import m from "mithril";

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

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<template>
  <div>${doubleCount}</div>
</template>

Templating

Minimal template

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import m from "mithril";

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

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

Styling

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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"),
      ),
  };
}

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.title {
  color: red;
}

Loop

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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)),
      ),
  };
}

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<template>
  <ul>
    <li repeat.for="color of colors">${color}</li>
  </ul>
</template>

Event click

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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"),
      ),
  };
}

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<template>
  <p>Counter: ${count}</p>
  <button click.trigger="incrementCount()">+1</button>
</template>

Dom ref

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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),
      }),
  };
}

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<template>
  <input ref="inputElement" />
</template>

Conditional

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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())),
      ),
  };
}

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<template>
  <button click.trigger="nextLight()">Next light</button>
  <p>Light is: ${light}</p>
  <p>
    You must
    <span if.bind="light === 'red'">STOP</span>
    <span if.bind="light === 'orange'">SLOW DOWN</span>
    <span if.bind="light === 'green'">GO</span>
  </p>
</template>

Lifecycle

On mount

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import m from "mithril";

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

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

On unmount

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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),
  };
}

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<template>
  <p>Current time: ${time}</p>
</template>

Component composition

Props

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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,
      }),
  };
}

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<template>
  <require from="./user-profile"></require>
  <user-profile
    name.bind="name"
    age.bind="age"
    favourite-colors.bind="colors"
    is-available.bind="available"
  ></user-profile>
</template>

Emit to parent

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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"),
    ),
});

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<template>
  <require from="./answer-button"></require>
  <p>Can I come ?</p>
  <answer-button action-handler.call="handleAnswer(reply)"></answer-button>
  <p style="font-size: 50px">${isHappy ? "😀" : "😥"}</p>
</template>

Slot

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

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

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<template>
  <require from="./funny-button"></require>

  <funny-button>Click me !</funny-button>
</template>

Slot fallback

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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")),
  };
}

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<template>
  <require from="./funny-button"></require>

  <funny-button></funny-button>
  <funny-button>Click me !</funny-button>
</template>

Context

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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 }),
      ),
  };
}

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Form input

Input text

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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 })),
  };
}

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<template>
  <p>${text}</p>
  <input value.bind="text" />
</template>

Checkbox

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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"),
      ),
  };
}

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

Radio

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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),
          ),
        ),
      ),
  };
}

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<template>
  <div>Picked: ${picked}</div>

  <input id="blue-pill" checked.bind="picked" type="radio" value="blue" />
  <label for="blue-pill">Blue pill</label>

  <input id="red-pill" checked.bind="picked" type="radio" value="red" />
  <label for="red-pill">Red pill</label>
</template>

Select

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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),
        ),
      ),
  };
}

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<template>
  <select value.bind="selectedColorId">
    <option value="">Select A Color</option>
    <option
      repeat.for="color of colors"
      value.bind="color.id"
      disabled.bind="color.isDisabled"
    >
      ${color.text}
    </option>
  </select>
</template>

Webapp features

Render app

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

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Fetch data

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

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<template>
  <p if.bind="isLoading">Fetching users...</p>
  <p if.bind="error">An error ocurred while fetching users</p>
  <ul if.bind="users">
    <li repeat.for="user of users">
      <img src.bind="user.picture.thumbnail" alt="user" />
      <p>${ user.name.first } ${ user.name.last }</p>
    </li>
  </ul>
</template>