JSFiddle - React, Tailwind, and code Playground

HTML

<form id="frm_items">
    <input type="text" name="txt_test" value="test text" /><br />
    <select id="customer_outlets" name="customer_outlets[]" multiple="multiple" size="15" style="width:360px"></select><br />
    <input type="button" id="btn_load_options" value="Load Options" /><br />
    <input type="submit" value="Submit/Serialize" />
</form>
<br />
<div id="display_serialized_options"></div>

JavaScript

$('#btn_load_options').click(function(){
    for (var i = 10000; i <= 13000; i++) {
        $('#customer_outlets').append('<option value="theverylongstinkinvalue'+i+'">Option '+i+'</option>');
    }
});

$('#frm_items').submit(function(){
    $('#customer_outlets option').prop('selected', true);
    var form_data = $(this).serialize();
    alert(form_data.length);
    $('#display_serialized_options').text(form_data);
    alert($('#display_serialized_options').text().length);
    return false;
});