To serve single page applications

main.go

package main

import (
	"log"
	"net/http"
)

func main() {
	h := http.FileServer(spaFileSystem{http.Dir("static")})

	log.Fatalln(http.ListenAndServe(":3000", h))
}

type spaFileSystem struct {
	fs http.FileSystem
}

// Open a file in the dir, falling back to index.html.
func (fs spaFileSystem) Open(name string) (http.File, error) {
	f, err := fs.fs.Open(name)
	if err != nil {
		return fs.fs.Open("index.html")
	}
	return f, nil
}