How to turn selected layers into symbols？

[kqskcm]

This feature is not available when using the old version of an，It can only be solved with this command，but having trouble with the code

var symbolName = prompt("Enter new graphic name");

if(symbolName != null) {
		
	var version = fl.version;
	var versionNum = parseInt(version.substring(version.indexOf(" "), version.indexOf(",")));
	
	var dom = fl.getDocumentDOM(); 
	var tl = dom.getTimeline(); 
	
	//create rectangle at top (guide for stage)
	var guideLayerNum = tl.addNewLayer('_stageGuide');
	tl.setSelectedLayers(guideLayerNum, true);
	
	var stroke = dom.getCustomStroke('toolbar');
	var strokeCopy = dom.getCustomStroke('toolbar');
	var fill = dom.getCustomFill('toolbar');
	var useCustomStroke = new Boolean();
	useCustomStroke = stroke.style == "noStroke" && fill.style == "noFill";
	if(useCustomStroke) { 
		//fillCopy.color = 0xffffff; //attempting to set this var crashes flash
		stroke.style = 'solid';
		stroke.thickness = 1;
		stroke.color = 0xff0000;	//deprecated as of CS3
		//stroke.shapeFill.color = 0xff0000; //(for next version of Flash)
		if(versionNum >= 8) stroke.scaleType ='none'; //flash 8 & above
		dom.setCustomStroke(stroke);
	}
	var w = parseInt(dom.width);
	var h = parseInt(dom.height);
	dom.addNewRectangle({left:0,top:0,right:w,bottom:h},0, false, false);
	tl.setLayerProperty('locked', true);
	tl.reorderLayer(guideLayerNum, 0, true);
	
	var frameSeq = tl.getSelectedFrames(); 
	var layerSeq = tl.getSelectedLayers(); 
	var lib = dom.library; 
	
	//clear [user] selected layers
	var selLayers = tl.getSelectedLayers();
	for(var i = 0; i < selLayers.length; i++){
		tl.setSelectedLayers(selLayers[i], true);
	}
	
	//clear [user] selected frames
	var clearFrameSel = new Array();
	for (var i = 0; i < frameSeq.length; i+=3){
		var tlayer = frameSeq[i];
		clearFrameSel.push(tlayer, -1, -1);
		tl.currentLayer = tlayer;
		tl.setSelectedLayers(tlayer, true);
	}
	
	tl.setSelectedFrames(clearFrameSel, true);
	var layerProps = new Array();
	
	//select all frames in timeline
	var endFrameArr = new Array();
	var frameSel = new Array();
	tl.expandFolder(true, true, -1); //expands all folders
	for (var i = 0; i < tl.layerCount; i++){
		var tlayer = tl.layers[i];
		var props = new Object();
		props.locked = tlayer.locked;
		props.visible = tlayer.visible;
		layerProps.push(props);
		frameSel.push(i, 0, tl.frameCount);
		endFrameArr.push(tlayer.frameCount);
		tl.currentLayer = tlayer;
		tl.setSelectedLayers(i, i==0);
	}
	
	tl.setSelectedFrames(frameSel, true);
	tl.copyFrames();
	
	//delete guide rectangle
	//tl.deleteLayer(0);
	

	if(symbolName == symbolName == "" || symbolName == undefined || symbolName.length < 1) symbolName = "_stageClip";
	
	lib.addNewItem('graphic', symbolName, 'top left');
	
	//dom.enterEditMode();
	lib.editItem(symbolName);
	var newTL = dom.getTimeline();
	newTL.selectAllFrames();
	newTL.pasteFrames();
	
	//add end frames & set layer props
	for (var i = 0; i < newTL.layerCount; i++){
		if(endFrameArr[i] < newTL.frameCount){
			newTL.setSelectedLayers(i, true);
			newTL.removeFrames(endFrameArr[i], newTL.frameCount);
		}
		newTL.layers[i].locked = layerProps[i].locked;
		newTL.layers[i].visible = layerProps[i].visible;
	}
	
	//set guide rectangle to outlines
	newTL.setSelectedLayers(0, true);
	newTL.setLayerProperty('outline', true);
	newTL.setLayerProperty('layerType',  'guide');
	
	//reset stroke color
	//if(useCustomStroke) {
		/*fl.trace('attempting to reset stroke');
		strokeCopy.style = "noStroke";
		strokeCopy.color = null;
		dom.setCustomStroke(strokeCopy);*/ //won't reset to null for some reason
	//}
	
	//return to main timeline
	dom.exitEditMode();
	tl = dom.getTimeline();

	for(var i=tl.layerCount; i > 0; i--){
		tl.currentLayer = i;
		tl.deleteLayer();
	}
	tl.currentLayer = 0;
	tl.setLayerProperty('locked', false);
	tl.setLayerProperty('name', symbolName);
	tl.selectAllFrames();
	tl.clearKeyframes();
	
	var newLayerNum = 0;
	lib.addItemToDocument({x:0, y:0}, symbolName);
	tl.insertFrames(newTL.frameCount);
	tl.layers[newLayerNum].frames[0].elements[0].symbolType = "graphic";
	tl.layers[newLayerNum].frames[0].elements[0].firstFrame = 0;
	tl.layers[newLayerNum].frames[0].elements[0].loop = "play once";
	tl.layers[newLayerNum].frames[0].elements[0].x = dom.width/2;
	tl.layers[newLayerNum].frames[0].elements[0].y = dom.height/2;

}

[n. tilcheff]

You can use Timeline Block To Symbol.

[kqskcm]

Hope to optimize the code I provided to achieve this functionality