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Detecting if data exists in Firebase [JavaScript]

Forked from How to use the jQuery $().ready function.

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sundip 66

published 4 years ago

    <!-- Installing Firebase from CDN -->
    <script src='https://cdn.firebase.com/v0/firebase.js'></script>
    <script type="text/javascript">
    /* Recipe code to check if data exists in Firebase */
      function go() {
        var userId = prompt('Username?', 'Guest');
      var USERS_LOCATION = 'https://SampleChat.firebaseIO-demo.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 Firebase(USERS_LOCATION);
        usersRef.child(userId).once('value', function(snapshot) {
          var exists = (snapshot.val() !== null);
          userExistsCallback(userId, exists);
    <link rel="stylesheet" href="runnable.css" />
    <h1>Check if a username exists in Firebase Chat example</h1>
    <p><a href="#" onclick="go();">Click here</a> to check if a username exists</p>
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