05 Browser interop

Gothic apps do not need to write JavaScript, but sometimes an app needs a browser API. The browser module is a small, curated Go surface for that. Every function is client-only and has a direct lowering in the generated JavaScript.

The module is separate from core gothic:

go get github.com/metruzanca/gothic/browser

import "github.com/metruzanca/gothic/browser"

Functions

browser.Alert("Saved")
browser.Log("loaded", count)
browser.SetTitle("Todos")

browser.SetItem("theme", "dark")
theme := browser.GetItem("theme")
browser.RemoveItem("theme")

browser.Copy("text to copy")
browser.Focus("#search")
height := browser.ClientHeight("#rows")
browser.Reload()

browser.Navigate("/about")
browser.Replace("/about")
browser.Back()

Function	Result
`Alert(message)`	Shows a browser alert
`Log(values...)`	Writes to the console
`SetTitle(title)`	Sets the document title
`GetItem(key)`	Reads `localStorage`, empty string when missing
`SetItem(key, value)`	Writes `localStorage`
`RemoveItem(key)`	Removes a `localStorage` key
`Copy(text)`	Writes text to the clipboard
`Focus(selector)`	Focuses the first matching element
`ClientHeight(selector)`	Reads an element height, or `0`
`Reload()`	Reloads the page
`Navigate(path)`	`pushState` and dispatch `LocationChanged`
`Replace(path)`	`replaceState` and dispatch `LocationChanged`
`Back()`	History back

Rules

Calls are only valid in Init, Update, or a command. Using one in a view is a compile error.
The Go stubs panic if they run on the server. The server never runs commands, so this is safe.
Navigate, Replace, and Back require a LocationChanged message.
The package does not expose arbitrary window access. Add a function here when an app genuinely needs a new browser API.

ClientHeight is useful for measurement commands:

type Measure struct{}

func (m Model) Update(msg gothic.Msg) (gothic.Model, gothic.Cmd) {
	switch msg.(type) {
	case Measure:
		return m, func() gothic.Msg {
			return Measured{Height: browser.ClientHeight("#rows")}
		}
	}
	return m, nil
}

What next

The browser module covers small DOM and history calls. The next chapter covers long lists with the separate virtual module: