Having 2 different values in one dropdown

Question

I have this dropdown in codeigniter Nama Barang. This is the code :

<div class="form-group">
    <label>Nama Barang</label>
    <div class="form-inline">
        <select id="nama" class="form-control namabarangsearch col-sm-10" name="name" required onchange="getNamaTransaksi()">
            <option value="">-- Nama Barang --</option>
            <?php

            foreach ($groups as $group) {
                echo '<option value="' . $group->stok. '" value="' . $group->name . '">' . $group->name . '. Stok : ' . $group->stok . '</option>';
            }
            ?>
        </select>
    </div>

    <small class="form-text text-muted" id="sisa"></small>
</div>

Then the script :

<script>
    function getNamaTransaksi() {
        var x = document.getElementById("nama").value;
        document.getElementById("sisa").innerHTML = "Nama barang : " + x;
    }
</script>

What should i do if i want to have 2 value from the option, so i can call it on the script? I've tried to do this :

<script>
    function getNamaTransaksi() {
        var x = document.getElementById("nama").value['$group->stok'];
        document.getElementById("sisa").innerHTML = "Nama barang : " + x;
    }
</script>

But it gives me undefined value. What am i doing wrong here? also sorry if my code is messy.