var phoneNumber = getPhoneNumberFromUserInput();
var appVerifier = window.recaptchaVerifier;
firebase.auth().signInWithPhoneNumber(phoneNumber, appVerifier)
.then(function (confirmationResult) {
// SMS sent. Prompt user to type the code from the message, then sign the
// user in with confirmationResult.confirm(code).
window.confirmationResult = confirmationResult;
}).catch(function (error) {