Sumator.html

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <h1>Submition</h1>

    <input type="number" id="firstNumber"/> +
    <input type="number" id="secondNumber"/> =
    <input type="number" id="result">
    <input type="button" id="calculateButton" value="Calculate">

    <script>
        function calculate() {
        let firstNumber =
          parseInt(document.getElementById("firstNumber").value);

        let secondNumber =
           parseInt(document.getElementById("secondNumber").value);

         document.getElementById("result").value =
             firstNumber + secondNumber;
        }

        let calculateButton = document.getElementById("calculateButton");

        calculateButton.addEventListener("click", calculate);
    </script>
</body>
</html>