getNewName.js

function getNewName(layerName){
	// Local Variables
	var docName;

	// Set docName to the source doc name
	docName = sourceDoc.name;

	// Set newName to empty string
	var newName = "";

	// Get the last underscore in the document name
	var underscore = docName.lastIndexOf('_');

	// Set newName to the docName from the first char to the last underscore
	newName += docName.substring(0,underscore);
	
	// Set newName to underscore + layerName
	newName += '_' + layerName;

	// Save in file at destFolder and newName
	saveInFile = new File(destFolder + '/' + newName);
	
	// Return saveInFile that creates file at folder path
	return saveInFile;

}