检查用户是否存在

check_user_exist.js

function go() {
  var userId = prompt('Username?', 'Guest');
  checkIfUserExists(userId);
}
 
var USERS_LOCATION = 'https://SampleChat.wilddogio.com/users';
 
function userExistsCallback(userId, exists) {
  if (exists) {
    alert('user ' + userId + ' exists!');
  } else {
    alert('user ' + userId + ' does not exist!');
  }
}
 
// Tests to see if /users/<userId> has any data. 
function checkIfUserExists(userId) {
  var usersRef = new Wilddog(USERS_LOCATION);
  usersRef.child(userId).once('value', function(snapshot) {
    var exists = (snapshot.val() !== null);
    userExistsCallback(userId, exists);
  });
}