The vertical property of the VTTCue interface is a string representing the cue's writing direction.

A string containing one of the following values:

"" (an empty string)

Represents a horizontal writing direction.

"rl"

Represents a vertical writing direction growing to the left.

"lr"

Represents a vertical writing direction growing to the right.

In the following example a new VTTCue is created, then the value of vertical is set to "rl". The value is then printed to the console.

let video = document.querySelector('video');
let track = video.addTextTrack("captions", "Captions", "en");
track.mode = "showing";

let cue1 = new VTTCue(0, 0.9, 'Hildy!');
cue1.vertical = 'rl';
console.log(cue1.vertical);

track.addCue(cue1);