code: function() {
    document.getElementById('sign-in-with-redirect').addEventListener(
        'click', signInWithRedirect);
    document.getElementById('sign-in-with-popup').addEventListener(
        'click', signInWithPopup);
    document.getElementById('sign-out').addEventListener('click', function() {
      firebase.auth().signOut();
    });
    document.getElementById('delete-account').addEventListener(
        'click', function() {
          deleteAccount();
        });
  
    document.getElementById('recaptcha-normal').addEventListener(
        'change', handleConfigChange);
    document.getElementById('recaptcha-invisible').addEventListener(
        'change', handleConfigChange);
    // Check the selected reCAPTCHA mode.
    document.querySelector(
        'input[name="recaptcha"][value="' + getRecaptchaMode() + '"]')
        .checked = true;
  
    document.getElementById('email-signInMethod-password').addEventListener(
        'change', handleConfigChange);
    document.getElementById('email-signInMethod-emailLink').addEventListener(
        'change', handleConfigChange);
    // Check the selected email signInMethod mode.
    document.querySelector(
        'input[name="emailSignInMethod"][value="' + getEmailSignInMethod() + '"]')
        .checked = true;
  }
docs: Initializes the app.