loader.css

.loader {
    position: absolute;
    top: 50%;
    left: 50%;
    margin-left: -50px;
    margin-top: -50px;

    border: 16px solid #f3f3f3;
    border-top: 16px solid #3498db;
    border-radius: 50%;
    width: 120px;
    height: 120px;
    animation: spin 2s linear infinite;
}

@keyframes spin {
    0% { transform: rotate(0deg); }
    100% { transform: rotate(360deg); }
}

spinner.go

package main

import (
	"github.com/siongui/godom/wasm"
)

type LoadingSpinner struct {
	Spinner wasm.Value
	_timer  int64
}

func NewSpinner() LoadingSpinner {
	element := wasm.Document.CreateElement("div")
	element.Set("className", "loader")
	return LoadingSpinner{
		Spinner: element,
		_timer:  0,
	}
}

func (s *LoadingSpinner) Show() {
	wasm.Document.Get("body").Call("prepend", s.Spinner)
}

func (s *LoadingSpinner) Hide() {
	wasm.Document.Get("body").Call("removeChild", s.Spinner)
}