Event System

Event System

Wails provides a unified event system for pub/sub communication. Emit events from anywhere, listen from anywhere—Go to JavaScript, JavaScript to Go, window to window—enabling decoupled architecture with typed events and lifecycle hooks.

Quick Start

Go (emit):

app.Event.Emit("user-logged-in", map[string]interface{}{
    "userId": 123,
    "name": "Alice",
})

JavaScript (listen):

import { Events } from '@wailsio/runtime'

Events.On("user-logged-in", (event) => {
    console.log(`User ${event.data.name} logged in`)
})

That’s it! Cross-language pub/sub.

Event Types

Custom Events

Your application-specific events:

// Emit from Go
app.Event.Emit("order-created", order)
app.Event.Emit("payment-processed", payment)
app.Event.Emit("notification", message)

// Listen in JavaScript
Events.On("order-created", handleOrder)
Events.On("payment-processed", handlePayment)
Events.On("notification", showNotification)

System Events

Built-in OS and application events:

import "github.com/wailsapp/wails/v3/pkg/events"

// Theme changes
app.Event.OnApplicationEvent(events.Common.ThemeChanged, func(e *application.ApplicationEvent) {
    if e.Context().IsDarkMode() {
        app.Logger.Info("Dark mode enabled")
    }
})

// Application lifecycle
app.Event.OnApplicationEvent(events.Common.ApplicationStarted, func(e *application.ApplicationEvent) {
    app.Logger.Info("Application started")
})

Window Events

Window-specific events:

window.OnWindowEvent(events.Common.WindowFocus, func(e *application.WindowEvent) {
    app.Logger.Info("Window focused")
})

window.OnWindowEvent(events.Common.WindowClosing, func(e *application.WindowEvent) {
    app.Logger.Info("Window closing")
})

Emitting Events

From Go

Basic emit:

app.Event.Emit("event-name", data)

With different data types:

// String
app.Event.Emit("message", "Hello")

// Number
app.Event.Emit("count", 42)

// Struct
app.Event.Emit("user", User{ID: 1, Name: "Alice"})

// Map
app.Event.Emit("config", map[string]interface{}{
    "theme": "dark",
    "fontSize": 14,
})

// Array
app.Event.Emit("items", []string{"a", "b", "c"})

To specific window:

window.EmitEvent("window-specific-event", data)

From JavaScript

import { Events } from '@wailsio/runtime'

// Emit to Go
Events.Emit("button-clicked", { buttonId: "submit" })

// Emit to all windows
Events.Emit("broadcast-message", "Hello everyone")

Listening to Events

In Go

Application events:

app.Event.On("custom-event", func(e *application.CustomEvent) {
    data := e.Data
    // Handle event
})

With type assertion:

app.Event.On("user-updated", func(e *application.CustomEvent) {
    user := e.Data.(User)
    app.Logger.Info("User updated", "name", user.Name)
})

Multiple handlers:

// All handlers will be called
app.Event.On("order-created", logOrder)
app.Event.On("order-created", sendEmail)
app.Event.On("order-created", updateInventory)

In JavaScript

Basic listener:

import { Events } from '@wailsio/runtime'

Events.On("event-name", (event) => {
    console.log("Event received:", event.data)
})

With cleanup:

const unsubscribe = Events.On("event-name", handleEvent)

// Later, stop listening
unsubscribe()

Multiple handlers:

Events.On("data-updated", updateUI)
Events.On("data-updated", saveToCache)
Events.On("data-updated", logChange)

One Time handlers:

Events.Once("data-updated", updateVariable)

System Events

Application Events

Common events (cross-platform):

import "github.com/wailsapp/wails/v3/pkg/events"

// Application started
app.Event.OnApplicationEvent(events.Common.ApplicationStarted, func(e *application.ApplicationEvent) {
    app.Logger.Info("App started")
})

// Theme changed
app.Event.OnApplicationEvent(events.Common.ThemeChanged, func(e *application.ApplicationEvent) {
    isDark := e.Context().IsDarkMode()
    app.Event.Emit("theme-changed", isDark)
})

// File opened
app.Event.OnApplicationEvent(events.Common.ApplicationOpenedWithFile, func(e *application.ApplicationEvent) {
    filePath := e.Context().OpenedFile()
    openFile(filePath)
})

Platform-specific events:

macOS

// Application became active
app.Event.OnApplicationEvent(events.Mac.ApplicationDidBecomeActive, func(e *application.ApplicationEvent) {
    app.Logger.Info("App became active")
})

// Application will terminate
app.Event.OnApplicationEvent(events.Mac.ApplicationWillTerminate, func(e *application.ApplicationEvent) {
    cleanup()
})

Windows

// Power status changed
app.Event.OnApplicationEvent(events.Windows.APMPowerStatusChange, func(e *application.ApplicationEvent) {
    app.Logger.Info("Power status changed")
})

// System suspending
app.Event.OnApplicationEvent(events.Windows.APMSuspend, func(e *application.ApplicationEvent) {
    saveState()
})

Linux

// Application startup
app.Event.OnApplicationEvent(events.Linux.ApplicationStartup, func(e *application.ApplicationEvent) {
    app.Logger.Info("App starting")
})

// Theme changed
app.Event.OnApplicationEvent(events.Linux.SystemThemeChanged, func(e *application.ApplicationEvent) {
    updateTheme()
})

Window Events

Common window events:

// Window focus
window.OnWindowEvent(events.Common.WindowFocus, func(e *application.WindowEvent) {
    app.Logger.Info("Window focused")
})

// Window blur
window.OnWindowEvent(events.Common.WindowBlur, func(e *application.WindowEvent) {
    app.Logger.Info("Window blurred")
})

// Window closing
window.OnWindowEvent(events.Common.WindowClosing, func(e *application.WindowEvent) {
    if hasUnsavedChanges() {
        e.Cancel()  // Prevent close
    }
})

// Window closed
window.OnWindowEvent(events.Common.WindowClosed, func(e *application.WindowEvent) {
    cleanup()
})

Event Hooks

Hooks run before standard listeners and can cancel events:

// Hook - runs first, can cancel
window.RegisterHook(events.Common.WindowClosing, func(e *application.WindowEvent) {
    if hasUnsavedChanges() {
        result := showConfirmdialog("Unsaved changes. Close anyway?")
        if result != "yes" {
            e.Cancel()  // Prevent window close
        }
    }
})

// Standard listener - runs after hooks
window.OnWindowEvent(events.Common.WindowClosing, func(e *application.WindowEvent) {
    app.Logger.Info("Window closing")
})

Key differences:

Feature	Hooks	Standard Listeners
Execution order	First, in registration order	After hooks, no guaranteed order
Blocking	Synchronous, blocks next hook	Asynchronous, non-blocking
Can cancel	Yes	No (already propagated)
Use case	Control flow, validation	Logging, side effects

Event Patterns

Pub/Sub Pattern

// Publisher (service)
type OrderService struct {
    app *application.Application
}

func (o *OrderService) CreateOrder(items []Item) (*Order, error) {
    order := &Order{Items: items}

    if err := o.saveOrder(order); err != nil {
        return nil, err
    }

    // Publish event
    o.app.Event.Emit("order-created", order)

    return order, nil
}

// Subscribers
app.Event.On("order-created", func(e *application.CustomEvent) {
    order := e.Data.(*Order)
    sendConfirmationEmail(order)
})

app.Event.On("order-created", func(e *application.CustomEvent) {
    order := e.Data.(*Order)
    updateInventory(order)
})

app.Event.On("order-created", func(e *application.CustomEvent) {
    order := e.Data.(*Order)
    logOrder(order)
})

Request/Response Pattern

// Frontend requests data
Emit("get-user-data", { userId: 123 })

// Backend responds
app.Event.On("get-user-data", func(e *application.CustomEvent) {
    data := e.Data.(map[string]interface{})
    userId := int(data["userId"].(float64))

    user := getUserFromDB(userId)

    // Send response
    app.Event.Emit("user-data-response", user)
})

// Frontend receives response
Events.On("user-data-response", (event) => {
    const user = event.data
    displayUser(user)
})

Note: For request/response, bindings are better. Use events for notifications.

Broadcast Pattern

// Broadcast to all windows
app.Event.Emit("global-notification", "System update available")

// Each window handles it
Events.On("global-notification", (event) => {
    const message = event.data
    showNotification(message)
})

Event Aggregation

type EventAggregator struct {
    events []Event
    mu     sync.Mutex
}

func (ea *EventAggregator) Add(event Event) {
    ea.mu.Lock()
    defer ea.mu.Unlock()

    ea.events = append(ea.events, event)

    // Emit batch every 100 events
    if len(ea.events) >= 100 {
        app.Event.Emit("event-batch", ea.events)
        ea.events = nil
    }
}

Complete Example

Go:

package main

import (
    "github.com/wailsapp/wails/v3/pkg/application"
    "github.com/wailsapp/wails/v3/pkg/events"
)

type NotificationService struct {
    app *application.Application
}

func (n *NotificationService) Notify(message string) {
    // Emit to all windows
    n.app.Event.Emit("notification", map[string]interface{}{
        "message":   message,
        "timestamp": time.Now(),
    })
}

func main() {
    app := application.New(application.Options{
        Name: "Event Demo",
    })

    notifService := &NotificationService{app: app}

    // System events
    app.Event.OnApplicationEvent(events.Common.ThemeChanged, func(e *application.ApplicationEvent) {
        isDark := e.Context().IsDarkMode()
        app.Event.Emit("theme-changed", isDark)
    })

    // Custom events from frontend
    app.Event.On("user-action", func(e *application.CustomEvent) {
        data := e.Data.(map[string]interface{})
        action := data["action"].(string)

        app.Logger.Info("User action", "action", action)

        // Respond
        notifService.Notify("Action completed: " + action)
    })

    // Window events
    window := app.Window.New()

    window.OnWindowEvent(events.Common.WindowFocus, func(e *application.WindowEvent) {
        app.Event.Emit("window-focused", window.Name())
    })

    window.RegisterHook(events.Common.WindowClosing, func(e *application.WindowEvent) {
        // Confirm before close
        app.Event.Emit("confirm-close", nil)
        e.Cancel()  // Wait for confirmation
    })

    app.Run()
}

JavaScript:

import { Events } from '@wailsio/runtime'

// Listen for notifications
Events.On("notification", (event) => {
    showNotification(event.data.message)
})

// Listen for theme changes
Events.On("theme-changed", (event) => {
    const isDark = event.data
    document.body.classList.toggle('dark', isDark)
})

// Listen for window focus
Events.On("window-focused", (event) => {
    const windowName = event.data
    console.log(`Window ${windowName} focused`)
})

// Handle close confirmation
Events.On("confirm-close", (event) => {
    if (confirm("Close window?")) {
        Emit("close-confirmed", true)
    }
})

// Emit user actions
document.getElementById('button').addEventListener('click', () => {
    Emit("user-action", { action: "button-clicked" })
})

Best Practices

✅ Do

• Use events for notifications - One-way communication
• Use bindings for requests - Two-way communication
• Keep event names consistent - Use kebab-case
• Document event data - What fields are included?
• Unsubscribe when done - Prevent memory leaks
• Use hooks for validation - Control event flow

❌ Don’t

• Don’t use events for RPC - Use bindings instead
• Don’t emit too frequently - Batch if needed
• Don’t block in handlers - Keep them fast
• Don’t forget to unsubscribe - Memory leaks
• Don’t use events for large data - Use bindings
• Don’t create event loops - A emits B, B emits A

Next Steps

Custom Events

Create your own event types.

Learn More →

Event Patterns

Common event patterns and best practices.

Learn More →

Bindings

Use bindings for request/response.

Learn More →

Window Events

Handle window lifecycle events.

Learn More →

---

Questions? Ask in Discord or check the event examples.