Select Last pattern

This should create a Pattern Layer with the last Pattern. 

// create pattern layer with last pattern;
// 2023, use it at your own risk;
if (app.documents.length > 0) {
try {
var ref = new ActionReference();
ref.putProperty(stringIDToTypeID ("property"), stringIDToTypeID("presetManager") ); 
ref.putEnumerated( charIDToTypeID("capp"), charIDToTypeID("Ordn"), charIDToTypeID("Trgt") );
var applicationDesc = executeActionGet(ref);
var presetManager = applicationDesc.getList(stringIDToTypeID("presetManager"));
var patternNames = presetManager.getObjectValue(4).getList(stringIDToTypeID("name"));
var theNames = new Array;
for (m = 0; m < patternNames.count; m++) {
    theNames.push(patternNames.getString(m))
};
makePatternLayer (theNames[theNames.length-1], 100);
//brickFill (theNames[theNames.length-1], 0.1)
} catch (e) {};
};
////// make pattern layer //////
function makePatternLayer (thePatternName, theScale) {
// =======================================================
var idMk = charIDToTypeID( "Mk  " );
	var desc3 = new ActionDescriptor();
	var idnull = charIDToTypeID( "null" );
		var ref1 = new ActionReference();
		var idcontentLayer = stringIDToTypeID( "contentLayer" );
		ref1.putClass( idcontentLayer );
	desc3.putReference( idnull, ref1 );
	var idUsng = charIDToTypeID( "Usng" );
		var desc4 = new ActionDescriptor();
		var idType = charIDToTypeID( "Type" );
			var desc5 = new ActionDescriptor();
			var idScl = charIDToTypeID( "Scl " );
			var idPrc = charIDToTypeID( "#Prc" );
			desc5.putUnitDouble( idScl, idPrc, theScale );
			var idPtrn = charIDToTypeID( "Ptrn" );
				var desc6 = new ActionDescriptor();
				var idNm = charIDToTypeID( "Nm  " );
				desc6.putString( idNm, "rust400x400" );
				var idIdnt = charIDToTypeID( "Nm  " );
				desc6.putString( idIdnt, thePatternName );
			var idPtrn = charIDToTypeID( "Ptrn" );
			desc5.putObject( idPtrn, idPtrn, desc6 );
		var idpatternLayer = stringIDToTypeID( "patternLayer" );
		desc4.putObject( idType, idpatternLayer, desc5 );
	var idcontentLayer = stringIDToTypeID( "contentLayer" );
	desc3.putObject( idUsng, idcontentLayer, desc4 );
executeAction( idMk, desc3, DialogModes.NO );
return app.activeDocument.activeLayer
};