From what I could find the window.open will return null when it fails to open. Something may be keeping the browser from opening additional windows a couple of times; maybe it is a popup blocker.

The actual loading of the url and creation of the window are done asynchronously.

https://developer.mozilla.org/en-US/docs/Web/API/Window.open

It is blocked by the browser. window.open is only not being blocked, when it is invoked by user action, for example in a click event, emitted by a native browser event. Also javaScript emitted events are being blocked, just like delayed setTimeout callbacks.

<a id="link" href="http://stackoverflow.com">StackOverflow</a>

<script type="text/javascript">

// Example (with jQuery for simplicity)

$("a#link").click(function (e) {
  e.preventDefault();

  var url = this.href;

  // this will not be blocked
  var w0 = window.open(url);
  console.log("w0: " + !!w0); // w0: true

  window.setTimeout(function () {
    // this will be blocked
    var w1 = window.open(url);
    console.log("w1: " + !!w1); // w1: false
  }, 5000);
});

</script>

Watch the Fiddle. I also tried it with the keypress event, but no luck.

window.open returns a valid reference to the new (or an existing named) window, or null when it failed to create a new window.

Do you have any extensions installed in the Microsoft Edge?

Try press Ctrl+Shift+N and it will open InPrivate browsing and see if the problem persist?

For IE10, window.open returns a NULL reference object if Enable Protected Mode is checked under Internet Options->Security->Security Level for this zone and the ZONE is different i.e. in my case local file opening a popup from Intranet.

window.open returns a reference object even if Enable Protected Mode is checked when yoursite.com opens someothersite.com in popup window i.e. Internet->Internet