How can I carry out a synchronous WebSocket connection

I wrote a piece of code that connects using WebSockets. However, when I am looking for the connection to close, it carries on with the execution without waiting for the connection to close. In other words the 'connection.onclose' is asynchronous, how can I make it synchronous? I don't code much in JavaScript. So I would find it very helpful if someone re-writes this piece of code in a synchronous way.

var connection = new WebSocket('wss://IP:PORT');
connection.onclose = function (event) {
    e = (event.code);

}
alert('message!')

JavaScript doesn't allow you to wait in synchronous code, so make it asynchronous. If you need it to be synchronous, then it is possible, but not ideal.
Synchronous

var connection = new WebSocket('wss://IP:PORT');
var e;
function nextstuff() {
    alert('message!');
};
connection.onclose = function (event) {
    e = (event.code);
    nextstuff();
};

Asynchronous

(async function() {
    var connection = new WebSocket('wss://IP:PORT');
    var e;
    await new Promise(function(res) {
        connection.onclose = function (event) {
            e = event.code;
            res(event);
        }
    });
    alert('message!');
})();