Clicker Simulator (test)

<html>
  <head>
    <title>Clicker Simulator</title>
    <script>
      // initialize variables for clicks and upgrades
      let clicks = 0;
      let upgrades = [0,0,0,0,0,0,0,0,0,0,0,0,0,0,0];

      // function to update clicks on click
      function clickUpdate() {
        clicks++;
        document.getElementById("clicks").innerHTML = clicks;
      }

      // function to handle rebirth
      function rebirth() {
        clicks = 0;
        upgrades = [0,0,0,0,0,0,0,0,0,0,0,0,0,0,0];
        document.getElementById("clicks").innerHTML = clicks;
        document.getElementById("upgrades").innerHTML = "0/15 upgrades purchased";
      }

      // function to handle upgrades
      function upgrade(index) {
        if (upgrades[index] == 0 && clicks >= 100) {
          clicks -= 100;
          upgrades[index] = 1;
          document.getElementById("clicks").innerHTML = clicks;
          document.getElementById("upgrades").innerHTML = upgrades.filter(x => x == 1).length + "/15 upgrades purchased";
        }
      }
    </script>
  </head>
  <body>
    <h1>Clicker Simulator</h1>
    <p>Clicks: <span id="clicks">0</span></p>
    <button onclick="clickUpdate()">Click</button>
    <button onclick="rebirth()">Rebirth</button>
    <p id="upgrades">0/15 upgrades purchased</p>
    <button onclick="upgrade(0)">Upgrade 1</button>
    <button onclick="upgrade(1)">Upgrade 2</button>
    <button onclick="upgrade(2)">Upgrade 3</button>
    <button onclick="upgrade(3)">Upgrade 4</button>
    <button onclick="upgrade(4)">Upgrade 5</button>
    <button onclick="upgrade(5)">Upgrade 6</button>
    <button onclick="upgrade(6)">Upgrade 7</button>
    <button onclick="upgrade(7)">Upgrade 8</button>
    <button onclick="upgrade(8)">Upgrade 9</button>
    <button onclick="upgrade(9)">Upgrade 10</button>
    <button onclick="upgrade(10)">Upgrade 11</button>
    <button onclick="upgrade(11)">Upgrade 12</button>
    <button onclick="upgrade(12)">Upgrade 13</button>
    <button onclick="upgrade(13)">Upgrade 14</button>
    <button onclick="upgrade(14)">Upgrade 15</button>
  </body>
</html>