Kalkulator mellom W og Kwh

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Kalkulator for omgjøring mellom Watt og KWh</title>
    <style>
        #inpKw{
            margin-left: 15px;
        }
        #inpW{
            margin-left: 9px;
        }
        #inpKwh{
            margin-left: 7px;
        }
    </style>
</head>
<body>
    <h1>Kalkulator for omgjøring mellom Watt og Kwh</h1>
<form id="frm">
        Watt: <input id="inpW" type="number">
        <br>
        Timer: <input id="inpTimer" type="number">
        <br>
        Kw: <input id="inpKw" type="number" disabled>
        <br>
        Khw: <input id="inpKwh" type="number">
    <br>
    <button id="btnSubmit">Regn om!</button>
</form>
    <button id="ca">Reset</button>
<script>
    let frm = document.getElementById("frm");
    let inpW = document.getElementById("inpW");
    let inpKw = document.getElementById("inpKw");
    let inpKwh = document.getElementById("inpKwh");
    let inpTimer = document.getElementById("inpTimer");
    let btnSubmit = document.getElementById("btnSubmit");
    let ca = document.getElementById("ca");

    frm.onsubmit = function (evt) {
        evt.preventDefault();
        if(inpKwh.value === ""){
            inpKwh.value = (inpW.value * inpTimer.value) / 1000;
            inpKw.value = inpW.value / 1000;
        }else if(inpW.value === ""){
            inpW.value = (inpKwh.value * 1000)/inpTimer.value;
            inpKw.value = inpKwh.value/inpTimer.value;
        }
    };
    ca.onclick = function () {
        inpKw.value = "";
        inpW.value = "";
        inpKwh.value = "";
        inpTimer.value = "";
    }
</script>
</body>
</html>