fido-3.js

function getAssertion() {
  try {
    var challenge = getChallengeFromServer(); 
    var allowList = 
          [
            {
              type: 'ScopedCred',
              id:  getCredentialID()
            }
          ];
    var timeout = { };
    var ext = { };

    window.webauthn.getAssertion(challenge, timeout, allowList, ext)
	.then(function(assertion) {
         // Send signed challenge and meta data to server
        sendToServer(assertion);
      }, function (e) {
        // No credential in the store. Fallback to password
	});    
  } catch (ex) {
    // Log failure
  }
}