Is it possible to make a layer mask with the current selection using extendscript?

Yes, but not with DOM code, you need AM code. I'll post the code shortly...

To add a reveal or hide mask from an active selection:

maskSelection("revealSelection");

function maskSelection(maskParameter) {
  // Parameter = "revealSelection" or "hideSelection"
	var s2t = function (s) {
		return app.stringIDToTypeID(s);
	};
	var descriptor = new ActionDescriptor();
	var reference = new ActionReference();
	descriptor.putClass( s2t( "new" ), s2t( "channel" ));
	reference.putEnumerated( s2t( "channel" ), s2t( "channel" ), s2t( "mask" ));
	descriptor.putReference( s2t( "at" ), reference );
	descriptor.putEnumerated( s2t( "using" ), s2t( "userMaskEnabled" ), s2t( maskParameter ));
	executeAction( s2t( "make" ), descriptor, DialogModes.NO );
}

https://gist.github.com/MarshySwamp/cbd0f135aa6ad089b053c80a2a02edaa

To add a "full" layer mask with no selection:

addMask("reveallAll");

function addMask(maskVisibility) {
    // maskVisibility = "revealAll" or "hideAll"
    var c2t = function (s) {
        return app.charIDToTypeID(s);
    };
    var s2t = function (s) {
        return app.stringIDToTypeID(s);
    };
    var descriptor = new ActionDescriptor();
    var reference = new ActionReference();
    descriptor.putClass(s2t("new"), s2t("channel"));
    reference.putEnumerated(s2t("channel"), s2t("channel"), s2t("mask"));
    descriptor.putReference(s2t("at"), reference);
    descriptor.putEnumerated(s2t("using"), c2t("UsrM"), s2t(maskVisibility));
    executeAction(s2t("make"), descriptor, DialogModes.NO);
}

https://gist.github.com/MarshySwamp/5eb4863d08335e870a53ef04ccb33916