puyopuyotetr.is/app/javascript/mastodon/is_mobile.js

const LAYOUT_BREAKPOINT = 1024;

export function isMobile(width, columns) {
  switch (columns) {
  case 'multiple':
    return false;
  case 'single':
    return true;
  default:
    return width <= LAYOUT_BREAKPOINT;
  }
};

const iOS = /iPad|iPhone|iPod/.test(navigator.userAgent) && !window.MSStream;

export function isIOS() {
  return iOS;
};