How to get a number value from an input field?

Question

I have some issues with calculating some stuff with JS and getting the right values out of the input fields (number). When I use this code it doesn't show anything. So what is wrong with my JS? Do I need to include a jQuery file?

Answer 1

You had some mistakes in your HTML, but here is a working JSFiddle: Fiddle

You you are trying to get elements by their ID, but you don't give them an ID you give them a Name. Also, stop using inline JavaScript calls; it is bad practice.

function Calculate() {
    var TotalProductionTime = document.getElementById("TotalProductionTime").value;
    var TotalProductionTimeInMinutes = TotalProductionTime * 60;
    var Breaks = document.getElementById("Breaks").value;
    var Malfunctions = document.getElementById("Malfunctions").value;
    var TheoreticalProductionTime = TotalProductionTimeInMinutes - Breaks - Malfunctions;

    document.getElementById("test").innerHTML = TheoreticalProductionTime;
}

<form id="frm1" action="Calculate.html">
    <table width="350px" border="1px">
        <tr>
            <th colspan="2">Availability</th>
        </tr>
        <tr>
            <td>Total Production Time</td>
            <td>
                <input type="number" id="TotalProductionTime" placeholder="">hours</td>
        </tr>
        <tr>
            <td>Breaks</td>
            <td>
                <input type="number" id="Breaks" placeholder="">minutes</td>
        </tr>
        <tr>
            <td>Malfunctions</td>
            <td>
                <input type="number" id="Malfunctions" placeholder="">minutes</td>
        </tr>
        <tr>
            <td>Theoretical production time:</td>
            <td>
                <p id="test"></p>
            </td>
        </tr>
    </table>
    <input type="button" onclick="Calculate()" value="calculate">
</form>