Duplicates a Layer within a pre-processing script

psDuplicate.jsx

function psDuplicate(sourceName,destName,vis,lock,showHide){
    //"HdAl" - Hide All; "RvlA" - Reveal All; "RvlS" - Reveal Selection  
    
    var doc = app.activeDocument;    
    
    if(doc.activeLayer.isBackgroundLayer){
        doc.activeLayer.duplicate();
        doc.layers.name = destName; //variable must be string
    } else {
        doc.layers.getByName(sourceName).duplicate();
        doc.layers.getByName(sourceName+" copy").name = destName; //variable must be string         
    }
   
    if(lock==true) {doc.layers.getByName(destName).allLocked = true} else {doc.layers.getByName(destName).allLocked = false;}
    if(vis==true)  {doc.layers.getByName(destName).visible = true} else {doc.layers.getByName(destName).visible = false;}    
    if(!showHide)  {showHide=null} else {psNewMask(showHide,destName);} 
}