JSFiddle - React, Tailwind, and code Playground

HTML

<button onclick="popup_context_menu_in_iframe()">
  popup menu
</button>
<br/><br/>
<iframe srcdoc="<p>Hello world!</p>">
</iframe>

JavaScript

function popup_context_menu_in_iframe()
{
	var $element = $('iframe').contents().find('p');
  
  var element = $element.get(0);

  if (window.CustomEvent) {
    element.dispatchEvent(new CustomEvent('contextmenu'));
  } else if (document.createEvent) {  
    var ev = document.createEvent('HTMLEvents');
    ev.initEvent('contextmenu', true, false);
    element.dispatchEvent(ev);
  } else { // Internet Explorer
    element.fireEvent('oncontextmenu');
  }
}