Trigger a Sheet alert

sheet.js

let sketch = require('sketch')
let document = sketch.getSelectedDocument()
let documentWindow = document.sketchObject.windowControllers()[0].window())

let mySheetWindow = NSWindow.alloc().initWithContentRect_styleMask_backing_defer(
    NSMakeRect(0, 0, 200, 100),
    (NSWindowStyleMaskTitled | NSWindowStyleMaskDocModalWindow),
    NSBackingStoreBuffered,
    true
)
let progressView = NSProgressIndicator
    .alloc()
    .initWithFrame(NSMakeRect(20, 20, 160, 12))
progressView.setControlTint(NSBlueControlTint)
progressView.startAnimation(true)
mySheetWindow.contentView().addSubview(progressView)

documentWindow.beginSheet_completionHandler(mySheetWindow, nil)
setTimeout(function() {
    documentWindow.endSheet(mySheetWindow)
}, 1000 * 5)