In the old (Ajax-centered, pre-jQuery, pre-promises) way of using JavaScript, you'd use XMLHttpRequest to load some content into your page. A call using this approach might look like this: var XMLHttpRequest xhttp = new XMLHttpRequest () ; // Code to set callback functions, define vars like myURL, etc. xhttp.open("GET", myURL, true); xhttp.send(); That last parameter in the call to the open() method is a boolean indicating whether the xhttp call should be asynchronous. What might happen if you called xhttp.open with a false flag, i.e., it's not asynchronous? Select the best answer. Any user interface events fired while open() is running will be discarded. The code will blow up the stack (i.e., the browser will abort the call). Only Ul events will be processed while you wait on the response from the external server. The rest of your code will be blocked while you wait on the response from the external server or the browser stops the call to the server with the "a script is taking too long to run" alert dialog box