First Widgets

Getting Started

Start by importing the singleton Astal.Application instance.

app.ts

import { App } from "astal/gtk3"

App.start({
    main() {
        // you will instantiate Widgets here
        // and setup anything else if you need
    }
})

After your bundle step run gjs -m app.js, and that's it! Now you have an Astal instance running written in TypeScript.

Root of every shell component: Window

Astal apps are composed of widgets. A widget is a piece of UI that has its own logic and style. A widget can be as small as a button or an entire bar. The top level widget is always a Window which will hold all widgets.

widget/Bar.tsx

function Bar(monitor = 0) {
    return <window className="Bar" monitor={monitor}>
        <box>Content of the widget</box>
    </window>
}

app.ts

import Bar from "./widget/Bar"

App.start({
    main() {
        Bar(0)
        Bar(1) // instantiate for each monitor
    },
})

Creating and nesting widgets

Widgets are JavaScript functions which return Gtk widgets, either by using JSX or using a widget constructor.

MyButton.tsx

function MyButton(): JSX.Element {
    return <button onClicked="echo hello">
        <label label="Click me!" />
    </button>
}

MyButton.ts

import { Widget } from "astal/gtk3"

function MyButton(): Widget.Button {
    return new Widget.Button(
        { onClicked: "echo hello" },
        new Widget.Label({ label: "Click me!" }),
    )
}

INFO

The only difference between the two is the return type. Using markup the return type is always Gtk.Widget (globally available as JSX.Element), while using constructors the return type is the actual type of the widget. It is rare to need the actual return type, so most if not all of the time, you can use markup.

Now that you have declared MyButton, you can nest it into another component.

function MyBar() {
    return <window>
        <box>
            Click The button
            <MyButton />
        </box>
    </window>
}

Notice that widgets you defined start with a capital letter <MyButton />. Lowercase tags are builtin widgets, while capital letter is for custom widgets.

Displaying Data

JSX lets you put markup into JavaScript. Curly braces let you “escape back” into JavaScript so that you can embed some variable from your code and display it.

function MyWidget() {
    const label = "hello"

    return <button>{label}</button>
}

You can also pass JavaScript to markup attributes

function MyWidget() {
    const label = "hello"

    return <button label={label} />
}

Conditional Rendering

You can use the same techniques as you use when writing regular JavaScript code. For example, you can use an if statement to conditionally include JSX:

function MyWidget() {
    let content

    if (condition) {
        content = <True />
    } else {
        content = <False />
    }

    return <box>{content}</box>
}

You can also inline a conditional ? (ternary) expression.

function MyWidget() {
    return <box>{condition ? <True /> : <False />}</box>
}

When you don’t need the else branch, you can also use a shorter logical && syntax:

function MyWidget() {
    return <box>{condition && <True />}</box>
}

INFO

As you can guess from the above snippet, falsy values are not rendered.

Rendering lists

You can use for loops or array map() function.

function MyWidget() {
    const labels = [
        "label1"
        "label2"
        "label3"
    ]

    return <box>
        {labels.map(label => (
            <label label={label} />
        ))}
    </box>
}

Widget signal handlers

You can respond to events by declaring event handler functions inside your widget:

function MyButton() {
    function onClicked(self: Widget.Button, ...args) {
        console.log(self, "was clicked")
    }

    return <button onClicked={onClicked} />
}

The handler can also be a string, which will get executed in a subprocess asynchronously.

function MyButton() {
    return <button onClicked="echo hello" />
}

INFO

Attributes prefixed with on will connect to a signal of the widget. Their types are not generated, but written by hand, which means not all of them are typed. Refer to the Gtk and Astal docs to have a full list of them.

How properties are passed

Using JSX, a custom widget will always have a single object as its parameter.

type Props = {
    myprop: string
    child?: JSX.Element // when only one child is passed
    children?: Array<JSX.Element> // when multiple children are passed
}

function MyWidget({ myprop, child, children }: Props) {
    //
}

// child prop of MyWidget is the box
return <MyWidget myprop="hello">
    <box />
</MyWidget>

// children prop of MyWidget is [box, box, box]
return <MyWidget myprop="hello">
    <box />
    <box />
    <box />
</MyWidget>

State management

The state of widgets are handled with Bindings. A Binding lets you connect the state of an object to a widget so it re-renders when that state changes.

Use the bind function to create a Binding object from a Variable or a regular GObject and one of its properties.

Here is an example of a Counter widget that uses a Variable as its state:

import { Variable, bind } from "astal"

function Counter() {
    const count = Variable(0)

    function increment() {
        count.set(count.get() + 1)
    }

    return <box>
        <label label={bind(count).as(num => num.toString())} />
        <button onClicked={increment}>
            Click to increment
        <button>
    </box>
}

INFO

Bindings have an .as() method which lets you transform the assigned value. In the case of a Label, its label property expects a string, so it needs to be turned to a string first.

TIP

Variables have a shorthand for bind(variable).as(transform)

const v = Variable(0)
const transform = (v) => v.toString()

return <box>
    {/* these two are equivalent */}
    <label label={bind(v).as(transform)} />
    <label label={v(transform)} />
</box>

Here is an example of a battery percent label that binds the percentage property of the Battery object from the Battery Library:

import Battery from "gi://AstalBattery"
import { bind } from "astal"

function BatteryPercentage() {
    const bat = Battery.get_default()

    return <label label={bind(bat, "percentage").as((p) => p * 100 + " %")} />
}

Dynamic children

You can also use a Binding for child and children properties.

const child = Variable(<box />)

return <box>{child}</box>

const num = Variable(3)
const range = (n) => [...Array(n).keys()]

return <box>
    {num(n => range(n).map(i => (
        <button>
            {i.toString()}
        <button/>
    )))}
<box>

TIP

Binding children of widgets will implicitly call .destroy() on widgets that would be left without a parent. You can opt out of this behavior by setting noImplicityDestroy property on the container widget.

INFO

The above example destroys and recreates every widget in the list every time the value of the Variable changes. There might be cases where you would want to handle child creation and deletion yourself, because you don't want to lose the inner state of widgets that does not need to be recreated. In this case you can create a custom reactive structure

When there is at least one Binding passed as a child, the children parameter will always be a flattened Binding<Array<JSX.Element>>. When there is a single Binding passed as a child, the child parameter will be a Binding<JSX.Element> or a flattened Binding<Array<JSX.Element>>.

import { type Binding } from "astal"

function MyContainer({ children }: {
    children?: Binding<Array<JSX.Element>>
}) {
    // children is a Binding over an Array of widgets
}

return <MyContainer>
    <box />
    {num(n => range(n).map(i => (
        <button>
            {i.toString()}
        <button/>
    )))}
    [
        [
            <button />
        ]
        <button />
    ]
</MyContainer>

INFO

You can pass the followings as children:

• widgets
• deeply nested arrays of widgets
• bindings of widgets,
• bindings of deeply nested arrays of widgets

falsy values are not rendered and anything not from this list will be coerced into a string and rendered as a label