how to solve In the "typewriter.jsfl" file，A javascript error has occured.

var doc = fl.getDocumentDOM();

doc.breakApart();
doc.distributeToLayers();
doc.selectAll();

var obs = doc.selection;
doc.getTimeline().insertFrames( obs.length * 2, true, 1);

var tl = doc.getTimeline();
var total = obs.length;
var i = total + 1;

while( i-- ){
tl.setSelectedLayers( total - i, true );
tl.cutFrames(0);
tl.pasteFrames( i * 2 );
tl.clearFrames(0, (i * 2));

}