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chrisaiv on 07/22/12

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Last Edited at 07/22/12 04:39am

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Firebase: Chat

Firebase: Leaderboard

/ Published in: JavaScript
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Easy-to-use leaderboard

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Copy this code and paste it in your HTML 
  1. <html>
  2. <head>
  3.   <title>Firebase Leaderboard Example</title>
  4.   <script type="text/javascript" src="http://static.firebase.com/demo/firebase.js"></script>
  5.   <script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.7.1/jquery.min.js"></script>
  6.   <link rel="stylesheet" type="text/css" href="http://www.firebase.com/css/example.css">
  7. </head>
  8. <body>
  9. <table id="leaderboardTable"></table>
  10. <input type="text" id="nameInput" placeholder="Name">
  11. <input type="text" id="scoreInput" placeholder="Score">
  12.  
  13. <div id="highestscore">
  14.   Highest Score so Far: <span id="highestScoreDiv"></span>
  15. </div>
  16.  
  17. <script type="text/javascript">
  18.   var LEADERBOARD_SIZE = 5;
  19.  
  20.   // Build some firebase references.
  21.   var rootRef = new Firebase('http://demo.firebase.com/guest253197899');
  22.   var scoreListRef = rootRef.child("scoreList");
  23.   var highestScoreRef = rootRef.child("highestScore");
  24.  
  25.   // Keep a mapping of firebase locations to HTML elements, so we can move / remove elements as necessary.
  26.   var htmlForPath = {};
  27.  
  28.   // Helper function that takes a new score snapshot and adds an appropriate row to our leaderboard table.
  29.   function handleScoreAdded(scoreSnapshot, prevScoreName) {
  30.     var newScoreRow = $("<tr/>");
  31.     newScoreRow.append($("<td/>").append($("<em/>").text(scoreSnapshot.val().name)));
  32.     newScoreRow.append($("<td/>").text(scoreSnapshot.val().score));
  33.  
  34.     // Store a reference to the table row so we can get it again later.
  35.     htmlForPath[scoreSnapshot.name()] = newScoreRow;
  36.  
  37.     // Insert the new score in the appropriate place in the table.
  38.     if (prevScoreName === null) {
  39.       $("#leaderboardTable").append(newScoreRow);
  40.     }
  41.     else {
  42.       var lowerScoreRow = htmlForPath[prevScoreName];
  43.       lowerScoreRow.before(newScoreRow);
  44.     }
  45.   }
  46.  
  47.   // Helper function to handle a score object being removed; just removes the corresponding table row.
  48.   function handleScoreRemoved(scoreSnapshot) {
  49.     var removedScoreRow = htmlForPath[scoreSnapshot.name()];
  50.     removedScoreRow.remove();
  51.     delete htmlForPath[scoreSnapshot.name()];
  52.   }
  53.  
  54.   // Create a view to only receive callbacks for the last LEADERBOARD_SIZE scores
  55.   var scoreListView = scoreListRef.limit(LEADERBOARD_SIZE);
  56.  
  57.   // Add a callback to handle when a new score is added.
  58.   scoreListView.on('child_added', function (newScoreSnapshot, prevScoreName) {
  59.     handleScoreAdded(newScoreSnapshot, prevScoreName);
  60.   });
  61.  
  62.   // Add a callback to handle when a score is removed
  63.   scoreListView.on('child_removed', function (oldScoreSnapshot) {
  64.     handleScoreRemoved(oldScoreSnapshot);
  65.   });
  66.  
  67.   // Add a callback to handle when a score changes or moves positions.
  68.   var changedCallback = function (scoreSnapshot, prevScoreName) {
  69.     handleScoreRemoved(scoreSnapshot);
  70.     handleScoreAdded(scoreSnapshot, prevScoreName);
  71.   };
  72.   scoreListView.on('child_moved', changedCallback);
  73.   scoreListView.on('child_changed', changedCallback);
  74.  
  75.   // When the user presses enter on scoreInput, add the score, and update the highest score.
  76.   $("#scoreInput").keypress(function (e) {
  77.     if (e.keyCode == 13) {
  78.       var newScore = Number($("#scoreInput").val());
  79.       var name = $("#nameInput").val()
  80.       $("#scoreInput").val("");
  81.  
  82.       if (name.length === 0)
  83.         return;
  84.  
  85.       var userScoreRef = scoreListRef.child(name);
  86.  
  87.       // Use setWithPriority to put the name / score in Firebase, and set the priority to be the score.
  88.       userScoreRef.setWithPriority({ name:name, score:newScore }, newScore);
  89.  
  90.       // Track the highest score using a transaction.  A transaction guarantees that the code inside the block is
  91.       // executed on the latest data from the server, so transactions should be used if you have multiple
  92.       // clients writing to the same data and you want to avoid conflicting changes.
  93.       highestScoreRef.transaction(function (currentHighestScore) {
  94.         if (currentHighestScore === null || newScore > currentHighestScore) {
  95.           // The return value of this function gets saved to the server as the new highest score.
  96.           return newScore;
  97.         }
  98.         // if we return with no arguments, it cancels the transaction.
  99.         return;
  100.       });
  101.     }
  102.   });
  103.  
  104.   // Add a callback to the highest score in Firebase so we can update the GUI any time it changes.
  105.   highestScoreRef.on('value', function (newHighestScore) {
  106.     $("#highestScoreDiv").text(newHighestScore.val());
  107.   });
  108.  
  109. </script>
  110. </body>
  111. </html>

URL: http://www.firebase.com/tutorial/#8

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