How do I prevent Google Chrome from blocking my popup?

Yes, popups should be a direct result of a user action. Doing them in ajax callback will not do the trick. Also, using async:false is bad - in FF it is known to block the whole browser. Think of some other way to do the check:

• it could be the first thing you do in the popup
• you can open the popup on click and manipulate it later when the callback fires
• you can require the user to click again some button to trigger the popup (probably the worst solution)
• you can do it on page load

Following up on Emil's excellent answer, "you can open the popup on click and manipulate it later when the callback fires". I used this implementation.

$('#attackButton').click(function() {

New code here

    var win = window.open('');
    window.oldOpen = window.open;
    window.open = function(url) { // reassignment function
        win.location = url;
        window.open = oldOpen;
        win.focus();
    }

end new code

    $.ajax({
        url: baseurl + '/index.php',
        data: { 'gameid': 618 },
        type: 'POST',
        success: function(data) {
            window.open('some url'); // will call reassignment function above 
        }
    });

    return false;
});

You can open a window that is not blocked just under the onclick event, if you open it on ajax call it is considered popup. However I used this method with success for some time to open a popup and not be blocked.

http://en.nisi.ro/blog/development/javascript/open-new-window-window-open-seen-chrome-popup/

In my case the window.open was launched inside a promise in angular, which turned the popup blocker on, my solution was:

$scope.gotClick = function(){

  var myNewTab = browserService.openNewTab();
  someService.getUrl().then(
    function(res){
      browserService. updateTabLocation(res.url, myNewTab);
    }
  );
};

browserService:

this.openNewTab = function(){
  var newTabWindow = $window.open();
  return newTabWindow;
}

this.updateTabLocation = function(tabLocation, tab) {
  if(!tabLocation){
    tab.close();
  }
  tab.location.href = tabLocation;
}

this is how you can open a new tab using the promise response and not invoking the popup blocker.