<div class="form-group col-md-2 field">
      <%= form.label :employee_id %>
      <%= form.collection_select :employee_id, Employee.all, :id, :full_name, include_blank: true, class: "form-control", :onchange=>"getEmployee()" %>
</div>
<div id="emp_adress"></div>

function getEmployee() {
    var selectedValue=document.getElementById("employee_id").id;
    document.getElementById("emp_address").innerHTML=selectedValue;
};