JXA (JavaScript for Automation) StatuBar applet example.

SoundcloudStatusBar.js

ObjC.import('Cocoa')
ObjC.import('WebKit')

App = Application.currentApplication()
App.includeStandardAdditions = true

MyAction = SimpleSubclass('Action', {
  quit(sender) {
    App.quit()
  },
  menuWillOpen(menu) {
    App.activate()
  },
})

MyWebView = WebView('https://soundcloud.com/')
MyWebView.frame = $.NSMakeRect(0, 0, 1024, 560)

MyWebViewItem = MenuItem('custom view', null, null)
MyWebViewItem.view = MyWebView

MyMenu = $.NSMenu.alloc.init
MyMenu.addItem( MyWebViewItem )
MyMenu.addItem( MenuItem() )
MyMenu.addItem( MenuItem('Quit', 'quit:', MyAction) )
MyMenu.delegate = MyAction

MyStatusItem = StatusItem()
MyStatusItem.title = '音雲'
MyStatusItem.menu = MyMenu

//=====================================================================

function MenuItem(title, action, target) {
  if (!title && !action && !target) return $.NSMenuItem.separatorItem
  let i = $.NSMenuItem.alloc.init
  i.title  = title
  i.action = action
  i.target = target
  return i
}

function StatusItem() {
  return $.NSStatusBar.systemStatusBar.statusItemWithLength($.NSVariableStatusItemLength)
}

function WebView(url) {
  let z = $.NSZeroRect
  let c = $.WKWebViewConfiguration.alloc.init
  let w = $.WKWebView.alloc.initWithFrameConfiguration(z, c)
  let u = $.NSURL.URLWithString(url)
  let r = $.NSURLRequest.requestWithURL(u)
  w.loadRequest(r)
  return w
}

function SimpleSubclass(_name, methods) {
  if ($[_name]) return $[_name].alloc.init
  let _methods = {}
  for (let m in methods) {
    _methods[m+':'] = {
      types: ['void', ['id']],
      implementation: methods[m],
    }
  }
  ObjC.registerSubclass({
    name: _name,
    methods: _methods,
  })
  return $[_name].alloc.init
}

if you want hide the dock icon, write to info.plist.

	<key>LSUIElement</key>
	<true/>