Moon

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Guide

This guide will introduce you to the basics of Moon while creating a simple todo application. Get started by installing Moon and adding the following to the <body> of an HTML file. You can also follow along and load the examples in the playground.

<div id="root"></div>

This is a root element where Moon's view driver will mount the view. Begin the script by importing the HTML elements from Moon's view driver that will be used in the view. A script can be added to a JavaScript file linked to the HTML page or a script tag.

const { div, h1, ul, li, input, button } = Moon.view.m;

For the following guide, along with the rest of the documentation, the above HTML and JavaScript is assumed.

After initializing the application, add the following to the script to display a basic todo list view.

const viewTodos = ({ data }) =>
    <ul children=(data.todos.map(todo =>
        <li>{todo}</li>
    ))/>;

Moon.use({
    data: Moon.data.driver,
    view: Moon.view.driver("#root")
});

Moon.run(() => {
    const data = {
        todo: "",
        todos: [
            "Learn Moon",
            "Take a nap",
            "Go Shopping"
        ]
    };

    return {
        data,
        view: <viewTodos data=data/>
    };
});

Try it!

First of all, the viewTodos function returns a view. It uses an HTML-like syntax for creating views based on components. In this case, the ul and li components. Rather than using the normal children syntax for ul, they are manually defined with an attribute. This attribute maps every single todo to an li element with the todo content as its text. Curly braces are used for interpolation {todo}.

Everything in the view language is extra syntax for function calls. In the end, it boils down to:

const viewTodos = ({ data }) =>
    ul({
        children: data.todos.map(todo =>
            li({ children: [Moon.view.m.text({ data: todo })] })
        )
    });

Next, Moon.use is called with an object. This is how Moon configures drivers, programs that give input from the real world and handle output to the real world. In our case, it is called with two properties: data and view.

The data input and output is handled by the Moon data driver, which gives data as input and can accept new data as output. It is responsible for storing data.

The view input and output is handled by the Moon view driver, which gives event information as input and can accept a new view as output. It is responsible for providing a functional interface to the DOM, and uses a virtual DOM under the hood. It is passed the #root element to tell it where to mount.

Now, an input can be added to the view to allow the user to create todos.

const viewTodos = ({ data }) =>
    <div>
        <input type="text" value=data.todo @input=updateTodo/>
        <button @click=createTodo>Create</button>

        <ul children=(data.todos.map(todo =>
            <li>{todo}</li>
        ))/>
    </div>;

The @ syntax in front of attribute names is for DOM events: in this case, the @input and @click events. The @input event runs a handler when the value of an input changes. The @click event runs a handler whenever there is a click.

The event handlers will then look like:

const updateTodo = ({ data, view }) => {
    const dataNew = { ...data, todo: view.target.value };

    return {
        data: dataNew,
        view: <viewTodos data=dataNew/>
    };
};

const createTodo = ({ data }) => {
    const dataNew = {
        todo: "",
        todos: [...data.todos, data.todo]
    };

    return {
        data: dataNew,
        view: <viewTodos data=dataNew/>
    };
};

The event handlers have the same structure as the function we passed to Moon.run. Every time Moon runs a function, it gives it inputs from drivers and expects outputs for drivers. Event handlers are no different.

For the updateTodo event handler, the view driver provides event data as input. Using this, new data is created with the updated todo. This new data is returned to the data driver to store, and the new view is returned to the view driver to update the DOM.

For the createTodo event handler, new data is created again. It has an empty todo to clear the input and new todos using the current value of data.todo. The new data and view are returned to their corresponding drivers to make changes to the real world.

Try it!

This guide resulted in an extremely basic todo application, but can be extended to support more features. Try the following exercises to test your knowledge:

By default, the playground has a fully functioning todo application that has a few more advanced features. Try extending it with what you've learned!