jsfl to be fixed

(function(){
	
	var doc = fl.getDocumentDOM();
	var tml = doc.getTimeline();

	main();

	function main(){
		var selection = tml.getSelectedFrames();
		var numFrames = parseInt( prompt( "Enter the number of frames to add or subtract:  " ) );
		if( isNaN( numFrames ) ){
			alert("Please enter a number");
			return;
		}
		var i, l, s, e, insFrm = Math.abs( numFrames );
		
		for( i = 0; i < selection.length; i +=3 ){
			l = selection[i], s = selection[i+1], e = selection[i+2];
			
			if( numFrames < 0 ){
				removeFrames( tml.layers[ l ], l, s, e, insFrm );
			}else{
				addFrames( tml.layers[ l ], l, s, e, insFrm );
			}
		}
		
		tml.setSelectedFrames([], true);		
	}
	function addFrames( xlayer, l, s, e, fn ){
		var f = e;
		while( f > s ){
			f = Math.max( s, getLayerPrevKey( xlayer, f ) );
			tml.setSelectedFrames( [ l, f, f+1 ], true );
			tml.insertFrames( fn );
		}
	}
	function removeFrames( xlayer, l, s, e, fn ){
		var f = e;
		while( f > s ){
			f = Math.max( s, getLayerPrevKey( xlayer, f ) );
			tml.currentLayer = l;
			tml.removeFrames( f+1, f+1+fn );
		}
	}
	function getLayerPrevKey( alayer, sf ){
		if( ! alayer ) return null;
		var fi = ( ( sf - 1 ) < 0 ) ? 0 : sf - 1;
		var fr = alayer.frames[ fi ];
		if( ! fr ) return null;
		return fr.startFrame;
	}

	
})();