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<!DOCTYPE html>
<html>
<head>
  <title>Storing a collection of unique functions</title>
  <meta charset="utf-8">
  <link rel="stylesheet" type="text/css" href="../assert.css">
  <script src="../assert.js"></script>
</head>
<body>
  <script>
    var store = {
      nextId: 1,
      cache: {},
      add: function(fn) {
        if (!fn.id) {
          fn.id = this.nextId++;
          this.cache[fn.id] = fn;
          return true;
        }
      }
    };

    function ninja(){}

    assert(store.add(ninja),
           "Function was safely added.");
    assert(!store.add(ninja),
           "But it was only added once.");
  </script>
</body>

</html>