check-registered-protocol.ts

// https://stackoverflow.com/questions/836777/how-to-detect-browsers-protocol-handlers
// https://jsfiddle.net/stefansundin/0uca4h2o/
function checkRegisteredProtocol(protocol: string) {
  const input = document.createElement('input');
  input.style.position = 'absolute';
  input.style.opacity = '0';
  document.body.appendChild(input);
  let isSupported = false;
  input.focus();
  input.onblur = () => isSupported = true;
  location.href = `${protocol}://test.com`;
  return new Promise(res => {
    setTimeout(() => {
      res(isSupported);
      document.body.removeChild(input);
    }, 300);    
  });
}