JSFiddle - React, Tailwind, and code Playground

HTML

<input type="checkbox" checked="checked" name="item[2001]" /><br>
<input type="checkbox" name="item[2005]" /><br>
<input type="checkbox" checked="checked" name="item[2090]" /><br>

JavaScript

var itemCheckedList = [];
$(function(){
    $('[name^="item"]').each(function(){
        if ($(this).prop('checked')) {
            var start = $(this).attr('name').indexOf('[')+1;
            var end = $(this).attr('name').indexOf(']');
            itemCheckedList.push($(this).attr('name').substring(start, end));        
        }
    });
    console.log(itemCheckedList);
});