JSFiddle - React, Tailwind, and code Playground

HTML

<select id="jobtype[]" class="dropDown" size="4" multiple="multiple" name="jobtype[]">
<option value="28">Activity staff/ Resort Rep</option>
<option value="1">Admin/ Secretarial/ Clerical</option>
<option value="2">Advertising/ Marketing/ PR</option>
<option value="29">Art/ Design</option>
<option value="30">Au Pair/ Nanny</option>
</select>

JavaScript

$(function () {
    $("#jobtype\\[\\] option").each(function()
            {
                //if ($(this).val() == 39)
                { 
                    $(this).attr('selected', 'selected');
                }

            });
  });