JSFiddle - React, Tailwind, and code Playground

HTML

<SELECT NAME="sel_current" MULTIPLE SIZE=10 width=200>
	<OPTION VALUE="1">1</OPTION>
	<OPTION VALUE="2" SELECTED>2</OPTION>
	<OPTION VALUE="3">3</OPTION>
	<OPTION VALUE="4">4</OPTION>
	<OPTION VALUE="5" selected>5</OPTION>
	<OPTION VALUE="6">6</OPTION>
	<OPTION VALUE="7">7</OPTION>
</SELECT>

<SELECT NAME="sel_current" SIZE="10" width="200" MULTIPLE>
	<OPTION VALUE="1">1</OPTION>
	<OPTION VALUE="2">2</OPTION>
	<OPTION VALUE="3" SELECTED>3</OPTION>
	<OPTION VALUE="4">4</OPTION>
	<OPTION VALUE="5">5</OPTION>
	<OPTION VALUE="6">6</OPTION>
	<OPTION VALUE="7" selected>7</OPTION>
</SELECT>

<SELECT NAME="sel_old" SIZE="10" width="200" MULTIPLE>
	<OPTION VALUE="1" SELECTED>1</OPTION>
	<OPTION VALUE="2">2</OPTION>
	<OPTION VALUE="3">3</OPTION>
	<OPTION VALUE="4">4</OPTION>
	<OPTION VALUE="5">5</OPTION>
	<OPTION VALUE="6">6</OPTION>
	<OPTION VALUE="7" selected>7</OPTION>
</SELECT>

<button id="testButton">Test</button>

JavaScript

$(document).ready(function() {
    var obj_List = {};

    $("#testButton").on('click', function(e) {
        getItems("sel_current");
        getItems("sel_old");
        
        console.log(obj_List);
    });
    
    function getItems (name) {
        var items = [];
        
        $("select[name='" + name + "']").each(function() {
            items.push($(this).val());
        });
        
        obj_List[name] = items;
    };
    
    $("select").on('change', function() {
        var name = $(this).attr("name");
        obj_List[name] = {};
        getItems(name);
        
        console.log(obj_List);
    });
});