I am trying to change the plot type for my Plotly JS code but it wont return a vale for the btn.selectedIndex.
const btn = document.getElementById('btn');
btn.addEventListener('change', () => {
var sel = btn.selectedIndex
if (sel == 1) {
data1['type'] = "markers",
data1['mode'] = "scatter"
} else if (sel == 2) {
data1['type'] = "bar"
}
})<select name="Plot Type" id="btn">
<option value="">--Choose Plot--</option>
<option value="">--markers--</option>
<option value="">--bar--</option>
</select>