The browser itself will decide when it's appropriate to open a new tab versus a new window, though you can influence its decision via browser settings. That being said, there are often times certain things we can do to encourage one way over the other. In this particular instance, I was able to get IE10 to open a window by passing along width and height values:
$("button").on("click", function () {
window.open("http://msdn.microsoft.com", "popup", "width=640,height=480");
});
Keep in mind that you ultimately have no control over whether something opens in a new tab, or a new window. That is entirely up to the user's machine; so don't bake any user experience dependencies into this assumption.