Value property should be set to get value
<select id="ddlViewBy">
<option value="1">test1</option>
<option value="2" selected="selected">test2</option>
<option value="3">test3</option>
</select>
var e = document.getElementById("ddlViewBy");
var strUser = e.options[e.selectedIndex].value;
var e = document.getElementById("ddlViewBy");
var strUser = e.options[e.selectedIndex].text;
OnChange
<div>
<select class="form-control form-control-sm" onchange="fn_stock_selected(this)" >
<option>Select Security</option>
{% for zrec in z_security %}
<option value="{{zrec.symbol}}">{{zrec.security}}</option>
{% endfor %}
</select>
</div>
<script>
function fn_stock_selected(zitem){
window.open('/security/details/'+ zitem.value +'/','_blank');
zitem.value = 'Select Security';
}
</script>