I tried using javascript to fetch user's selection on a drop down selection inside Odoo's website, but I got the error in the title while doing it. Here is my code:



JS:
odoo.define("my-module.Custom", function (require) {
    "use strict";
    var ajax = require("web.ajax");
    var value = document.getElementById("selection").value;

    return ajax.jsonRpc("/shop/cart/update_json", "call", {
       'value': value,
    })
});


Part of XML:
select class="selection" name="selection" id="selection"
    option selected="true" t-att-value="line.some_fields" t-esc="line.some_fields"/
     t-foreach="request.env['res.partner'].sudo().search([])" t-as="x"
         t-foreach="x.subpoint_id" t-as="y"
             t-if="y.name"
                 t-if="(request.env.user.partner_id.member_id in y.name)"
                    t t-set="current_alloc" t-value="y.name"/
                    option t-att-value="y.name" t-esc="y.name"/
                /
            /
        /
    /
/select

Part of Controller (inheriting WebsiteSales):
_logger.info("Test")
value = kw.get("value")
if value:
	_logger.info("Test1")
	abc = 0
	for line in request.website.sale_get_order(force_create=True).order_line:
		_logger.info(abc)
		abc += 1
		line.write({
			'some_field': value
		})


In the code above, my drop down selection doesnt seem to grab the user's selection upon a change, and it gives me error when I click add/subtract product quantity more than once.



Error: 

UncaughtClientError

Uncaught Javascript Error > Service my-script already defined

Error: Service my-script already defined
    at odoo.define 
    at :1:6
    at DOMEval 
    at Function.globalEval 
    at text script 
    at ajaxConvert 
    at done 
    at XMLHttpRequest. 
    at Object.send 
    at Function.ajax