Replicating Sketch's Preview window

Load Preview.js

let previewWindow = NSApplication.sharedApplication().windows().find(window => window.title() == 'Preview')
let webview = previewWindow.contentView().subviews()[1] // need to launch sketch preview in order to find the proper webview and to start up the sketch server

let threadDictionary = NSThread.mainThread().threadDictionary()
let panelID = "com.testPanel"

if (threadDictionary[panelID]) {
  let panel = threadDictionary[panelID]
  panel.close()
  threadDictionary.removeObjectForKey(panelID)
}

var panelWidth = 312
var panelHeight = 210
let panel = NSPanel.alloc().init()
panel.setFrame_display(NSMakeRect(0, 0, panelWidth, panelHeight), true)
panel.setStyleMask(NSTexturedBackgroundWindowMask | NSTitledWindowMask | NSClosableWindowMask)
panel.title = "Testing"

panel.center()
panel.makeKeyAndOrderFront(null)
panel.setLevel(NSFloatingWindowLevel)

panel.standardWindowButton(NSWindowMiniaturizeButton).setHidden(true)
panel.standardWindowButton(NSWindowZoomButton).setHidden(true)

threadDictionary[panelID] = panel

//Setup
let frame = NSMakeRect(0,0,panelWidth,panelHeight)
let webviewConfig = webview.configuration().copy()
let newWebview = MSMirrorWebView.alloc().initWithFrame_configuration(frame,webviewConfig)
let url = webview.URL()
let request = NSURLRequest.alloc().initWithURL(url)
newWebview.loadRequest(request)

panel.contentView().addSubview(newWebview)