As for an opacity slider

I have a UI dialog script and I would like it to modify the opacity of two layers ... Layer 1 & Layer 2 How to put opacity on a slider? See the example I have;

// DIALOG
// ======
var dialog = new Window("dialog");
dialog.text = "Opacity";
dialog.orientation = "column";
dialog.alignChildren = ["center","top"];
dialog.spacing = 10;
dialog.margins = 16;

var statictext1 = dialog.add("statictext", undefined, undefined, {name: "statictext1"});
statictext1.text = "OPACITY LAYER 1";

var slider1 = dialog.add("slider", undefined, undefined, undefined, undefined, {name: "slider1"});
slider1.minvalue = 0;
slider1.maxvalue = 100;
slider1.value = 50;
slider1.preferredSize.width = 278;

var statictext2 = dialog.add("statictext", undefined, undefined, {name: "statictext2"});
statictext2.text = "OPACITY LAYER 2";

var slider2 = dialog.add("slider", undefined, undefined, undefined, undefined, {name: "slider2"});
slider2.minvalue = 0;
slider2.maxvalue = 100;
slider2.value = 50;
slider2.preferredSize.width = 278;

dialog.show();

create by SCRIPT DIALOG BUILDER
Can someone help me?