Open new tab with specific content to print hangs

I need to take specific div and open it in a new tab to print it.

It correctly opens the new tab, copies the div into it, but then it hangs - the loading/spinning icon on the tab sits there until I press Esc key to cancel the load - and THEN the print dialog opens:

var originalHtml = document.body.innerHTML;
printContent = document.getElementById(divId).innerHTML;

var printWin =;

Any ideas why its not just auto opening the print dialog, what's causing the hang ?