html

<label for="fuel">Current fuel level:</label>
<meter
  id="fuel"
  min="0"
  max="100"
  low="15"
  high="66"
  optimum="80"
  value="50"></meter>

js

const meterElement = document.getElementById("fuel");
console.log(meterElement.max); // 100
--meterElement.max;
console.log(meterElement.max); // 99