How to use form select value to action method (without query) - html

Question

I'm using pug to render some pages for my nodeJS server. In this case I'm trying to use the value captured in the form select in order to change the action method.
So, the idea is use the group name selected to go to that page:
form.w3-container(action="http://localhost:5004/groups/" + (option selected down below) method="GET")
select.form-control(data-toggle='select' class="form-control" data-placeholder='Disabled results')
option group1
option group2
option group3
button.btn.btn-success(type='submit') Go
Any suggestion on how can I do this, if possible without jquery (if it is not possible without I, an explanation on how to "use" it would be very much appreciated).
From what Shoaib said in this post, it should be possible, but I dint't quit understand his suggestion, poor context :/

Answer 1

HTML code:
<form id="myForm" class="w3-container" action="" method="POST">
<select id="mySelector" data-toggle='select' class="form-control" data-placeholder='Disabled results'>
<option value="">Select</option>
<option value="group1">group1</option>
<option value="group2">group2</option>
<option value="group3">group3</option>
</select>
</form>
ECMAscript code:
var selector = document.getElementById("mySelector");
selector.addEventListener("change", function() {
changeAction();
});
function changeAction() {
var finalAction = document.getElementById("myForm").action = "http://localhost:5004/groups/" + selector.value;
}
JSFiddle: https://jsfiddle.net/ytvhqrs0/1/