astal/docs/ags/first-widgets.md

First Widgets

AGS is the predecessor of Astal, which was written purely in TypeScript and so only supported JavaScript/TypeScript. Now it serves as a scaffolding tool for Astal projects in TypeScript. While what made AGS what it is, is now part of the Astal project, for simplicity we will refer to the Astal TypeScript lib as AGS.

:::tip If you are not familiar with the JavaScript syntax MDN and javascript.info have great references. :::

Getting Started

Start by initializing a project

ags --init

then run ags in the terminal

ags

Done! You have now a custom written bar using Gtk.

:::tip AGS will transpile every .ts, .jsx and .tsx files into regular javascript then it will bundle everything into a single javascript file which then GJS can execute. The bundler used is esbuild. :::

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.

::: code-group

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

:::

::: code-group

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.

:::code-group

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

import { Widget } from "astal"

function MyButton(): Widget.Button {
    return Widget.Button({
        onClicked: "echo hello",
        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 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 to the user.

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 one GObject to another, in our case it is used to rerender part of a widget based on the state of a GObject. A GObject can be a Variable or it can be from a Library.

We 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>

:::warning Only bind children of the box widget. Gtk does not cleanup widgets by default, they have to be explicitly destroyed. The box widget is a special container that will implicitly call .destroy() on its removed child widgets. You can disable this behavior by setting the noImplicityDestroy property. :::

:::info The above example destroys and recreates every widget in the list everytime the value of the Variable changes. There might be cases where you would want to handle child creation yourself, because you don't want to lose the inner state of widgets that does not need to be recreated. :::

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

function MyContainer({ children }) {
    // 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 :::