01.SumElements

<!DOCTYPE html>
<html lang="en">
    <head>
        <meta charset="UTF-8">
        <title>Homework-DOM</title>
    </head>

    <body>
    <input type="text" id="num1" /> +
    <input type="text" id="num2" /> =
    <input type="text" id="sum" readonly="readonly" />

    <input type="button" value="Calc" onclick="calc()" />
    <script>
        function calc() {
            let num1 = Number(document.getElementById('num1').value);
            let num2 = Number(document.getElementById('num2').value);
            let sum = num1 + num2;
            let sumInput = document.getElementById('sum');
            sumInput.value = sum;
        }
    </script>

    </body>
</html>