Bubble Tea

The fun, functional and stateful way to build terminal apps. A Go framework based on The Elm Architecture. Bubble Tea is well-suited for simple and complex terminal applications, either inline, full-window, or a mix of both.

Bubble Tea is in use in production and includes a number of features and performance optimizations we’ve added along the way. Among those is a high-performance cell-based renderer, built-in color downsampling, declarative views, high-fidelity keyboard and mouse handling, native clipboard support, and more.

To get started, see the tutorial below, the examples, the docs, and some common resources.

[!TIP]

Upgrading from v1? Check out the upgrade guide, or point your LLM at it and let it go to town.

By the way

Be sure to check out [Bubbles][bubbles], a library of common UI components for Bubble Tea.

Tutorial

Bubble Tea is based on the functional design paradigms of The Elm Architecture, which happens to work nicely with Go. It's a delightful way to build applications.

This tutorial assumes you have a working knowledge of Go.

By the way, the non-annotated source code for this program is available on GitHub.

Enough! Let's get to it.

For this tutorial, we're making a shopping list.

To start we'll define our package and import some libraries. Our only external import will be the Bubble Tea library, which we'll call tea for short.

package main

// These imports will be used later in the tutorial. If you save the file
// now, Go might complain they are unused, but that's fine.
// You may also need to run `go mod tidy` to download bubbletea and its
// dependencies.
import (
    "fmt"
    "os"

    tea "charm.land/bubbletea/v2"
)

Bubble Tea programs are comprised of a model that describes the application state and three simple methods on that model:

Init, a function that returns an initial command for the application to run.
Update, a function that handles incoming events and updates the model accordingly.
View, a function that renders the UI based on the data in the model.

The Model

So let's start by defining our model which will store our application's state. It can be any type, but a struct usually makes the most sense.

type model struct {
    choices  []string           // items on the to-do list
    cursor   int                // which to-do list item our cursor is pointing at
    selected map[int]struct{}   // which to-do items are selected
}

Initialization

Next, we’ll define our application’s initial state. Init can return a Cmd that could perform some initial I/O. For now, we don’t need to do any I/O, so for the command, we’ll just return nil, which translates to “no command.”

func initialModel() model {
	return model{
		// Our to-do list is a grocery list
		choices:  []string{"Buy carrots", "Buy celery", "Buy kohlrabi"},

		// A map which indicates which choices are selected. We're using
		// the  map like a mathematical set. The keys refer to the indexes
		// of the `choices` slice, above.
		selected: make(map[int]struct{}),
	}
}

After that, we’ll define our application’s initial state in the Init method. Init can return a Cmd that could perform some initial I/O. For now, we don't need to do any I/O, so for the command, we'll just return nil, which translates to "no command."

func (m model) Init() tea.Cmd {
    // Just return `nil`, which means "no I/O right now, please."
    return nil
}

The Update Method

Next up is the update method. The update function is called when “things happen.” Its job is to look at what has happened and return an updated model in response. It can also return a Cmd to make more things happen, but for now don't worry about that part.

In our case, when a user presses the down arrow, Update’s job is to notice that the down arrow was pressed and move the cursor accordingly (or not).

The “something happened” comes in the form of a Msg, which can be any type. Messages are the result of some I/O that took place, such as a keypress, timer tick, or a response from a server.

We usually figure out which type of Msg we received with a type switch, but you could also use a type assertion.

For now, we'll just deal with tea.KeyPressMsg messages, which are automatically sent to the update function when keys are pressed.

func (m model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
    switch msg := msg.(type) {

    // Is it a key press?
    case tea.KeyPressMsg:

        // Cool, what was the actual key pressed?
        switch msg.String() {

        // These keys should exit the program.
        case "ctrl+c", "q":
            return m, tea.Quit

        // The "up" and "k" keys move the cursor up
        case "up", "k":
            if m.cursor > 0 {
                m.cursor--
            }

        // The "down" and "j" keys move the cursor down
        case "down", "j":
            if m.cursor < len(m.choices)-1 {
                m.cursor++
            }

        // The "enter" key and the space bar toggle the selected state
        // for the item that the cursor is pointing at.
        case "enter", "space":
            _, ok := m.selected[m.cursor]
            if ok {
                delete(m.selected, m.cursor)
            } else {
                m.selected[m.cursor] = struct{}{}
            }
        }
    }

    // Return the updated model to the Bubble Tea runtime for processing.
    // Note that we're not returning a command.
    return m, nil
}

You may have noticed that <kbd>ctrl+c</kbd> and <kbd>q</kbd> above return a tea.Quit command with the model. That’s a special command which instructs the Bubble Tea runtime to quit, exiting the program.

The View Method

At last, it’s time to render our UI. Of all the methods, the view is the simplest. We look at the model in its current state and use it to build a tea.View. The view declares our UI content and, optionally, terminal features like alt screen mode, mouse tracking, cursor position, and more.

Because the view describes the entire UI of your application, you don’t have to worry about redrawing logic and stuff like that. Bubble Tea takes care of it for you.

func (m model) View() tea.View {
    // The header
    s := "What should we buy at the market?\n\n"

    // Iterate over our choices
    for i, choice := range m.choices {

        // Is the cursor pointing at this choice?
        cursor := " " // no cursor
        if m.cursor == i {
            cursor = ">" // cursor!
        }

        // Is this choice selected?
        checked := " " // not selected
        if _, ok := m.selected[i]; ok {
            checked = "x" // selected!
        }

        // Render the row
        s += fmt.Sprintf("%s [%s] %s\n", cursor, checked, choice)
    }

    // The footer
    s += "\nPress q to quit.\n"

    // Send the UI for rendering
    return tea.NewView(s)
}

All Together Now

The last step is to simply run our program. We pass our initial model to tea.NewProgram and let it rip:

func main() {
    p := tea.NewProgram(initialModel())
    if _, err := p.Run(); err != nil {
        fmt.Printf("Alas, there's been an error: %v", err)
        os.Exit(1)
    }
}

What’s Next?

This tutorial covers the basics of building an interactive terminal UI, but in the real world you'll also need to perform I/O. To learn about that have a look at the Command Tutorial. It's pretty simple.

There are also several Bubble Tea examples available and, of course, there are Go Docs.

Debugging

Debugging with Delve

Since Bubble Tea apps assume control of stdin and stdout, you’ll need to run delve in headless mode and then connect to it:

# Start the debugger
$ dlv debug --headless --api-version=2 --listen=127.0.0.1:43000 .
API server listening at: 127.0.0.1:43000

# Connect to it from another terminal
$ dlv connect 127.0.0.1:43000

If you do not explicitly supply the --listen flag, the port used will vary per run, so passing this in makes the debugger easier to use from a script or your IDE of choice.

Additionally, we pass in --api-version=2 because delve defaults to version 1 for backwards compatibility reasons. However, delve recommends using version 2 for all new development and some clients may no longer work with version 1. For

Bubbletea

Install / Use

README