Async function does not take affect

[hevilhuy]

This is the reproduce code:
let winbox = new WinBox(title,
{
html: rootElement.innerHTML,
onclose: async function (force)
{
return false;
},
}

If I change to the below then it works=

let winbox = new WinBox(title,
    {
        html: rootElement.innerHTML,
        onclose: function (force)
        {
            return false;
        },
     }

[jddurand]

I forked an async version at https://github.com/jddurand/winbox/tree/async - not beeing a js expert this is with no guarantee.
Webpack not done, you have to grab from src.
Tested with blazor and works fine with me.