How to prevent autoplay on mobile

Look at framer.com on desktop: the promo video autoplays. Look at it on mobile: it embeds as an ordinary YouTube video, with a manual play button. The behavior is different because video autoplay on mobile is much more annoying: video takes a big bite into your mobile data usage.

How does framer.com achieve this? By switching on whether the user-agent suggests that the device is a mobile. Here’s some equivalent code:

function isMobile() {
    return /Android|webOS|iPhone|iPad|iPod|BlackBerry|IEMobile|Opera Mini/i.test(navigator.userAgent);
}