via

Live web UI in Go. A page is a struct, a click is a method call, and the server can push the change to every open tab. No JavaScript to write, no build step.

via needs Go 1.27 or newer.

go mod init example.com/counter
go get github.com/go-via/via

main.go:

package main

import (
	"log"
	"net/http"
	"sync"

	"github.com/go-via/via"
	"github.com/go-via/via/h"
	"github.com/go-via/via/on"
	"github.com/go-via/via/topic"
)

var (
	mu    sync.Mutex
	count int64
	moved = topic.New[int64]()
)

func add(n int64) {
	mu.Lock()
	defer mu.Unlock()
	count += n
	moved.Publish(count)
}

func load() int64 {
	mu.Lock()
	defer mu.Unlock()
	return count
}

type Counter struct{ N via.State[int64] }

func (c *Counter) Inc(ctx *via.Ctx) { add(1) }
func (c *Counter) Dec(ctx *via.Ctx) { add(-1) }

func (c *Counter) View() h.H {
	return h.Div(
		h.Button(on.Click(c.Dec), h.Str("-")),
		h.H1(c.N.Display()),
		h.Button(on.Click(c.Inc), h.Str("+")),
	)
}

func main() {
	r := via.Handler(Counter{N: via.StateTrack(moved, load)})
	log.Fatal(http.ListenAndServe(":8080", r))
}

go run .

Open http://localhost:8080 in two tabs and click + in one. Both update. At startup via warns that no WithTrustedOrigin is set; Security covers what to set before you deploy. Getting started builds up to this program.

• Actions are methods. on.Click(c.Inc) takes a method value, so a misspelled action is a compile error, not a dead button.
• Live only where it needs to be. A page is plain HTTP until something on it goes live; then its tab holds one stream. Live state
• Nothing to build. The browser client ships inside the module, and the markup is Go.
• Testable from go test. Package vt drives pages, actions and live streams without a browser. Testing

Live state is held on the server. What it costs lists the tradeoffs.

• Getting started
• Tutorial
• Examples, with their source in internal/example
• API reference, and pkg.go.dev
• Deploy
• Security
• MIGRATION.md for upgrading between releases, and Migrating for v0.7 to v0.8

Pre-1.0: the API can change between minor versions. CHANGELOG.md records each release.

./ci.sh

It runs gofmt, vet, staticcheck and the race tests for via and the site module (internal/site), then the browser tier in vtbrowser, which needs Chromium or Chrome; --no-browser skips it. It reports, never rewrites.

CONVENTIONS.md has the code and test conventions, including the bar for a new duck-typed method.

MIT, see LICENSE.