JSFiddle - React, Tailwind, and code Playground

HTML

<form name="mmForm">
    <label for="element1">E1</label>
    <input type="text" id="element1">
    <label for="element2">E2</label>
    <input type="text" id="element2">
    <input type="button" value="Calculate" onclick="procesForm_mm();">
    <div id="resultfield_mm">Result:</div>
</form>

JavaScript

function procesForm_mm() {
        var e1 = document.mmForm.element1.value;
        var e2 = document.mmForm.element2.value;
        result_mm = parseInt(tabelPeriodic[e1].A) + parseInt(tabelPeriodic[e2].A);
        document.getElementById("resultfield_mm").innerHTML += result_mm;
    }
    var tabelPeriodic = [];

    tabelPeriodic["Fe"] = new Object();
    tabelPeriodic["Co"] = new Object();

    var el = tabelPeriodic["Fe"];
    el.denumire = "Fier";
    el.A = 56;
    el.Z = 26;
    el.grupa = "VIIIB";
    el.perioada = 4;

    el = tabelPeriodic["Co"];
    el.denumire = "Cobalt";
    el.A = 59;
    el.Z = 27;
    el.grupa = "IXB";
    el.perioada = 4;