header.php

<script async type="text/javascript"> 
 
function loadDynamicCategories() {

    $.getJSON('http://www.example.com/wp-admin/admin-ajax.php?action=wpl_ebay_store_categories&callback=?', function(data) {
        $('#categories_wrapper').append('<ul></ul>');
        $.each(data, function(index) {
    		$('#categories_wrapper ul').append('<li id="'+data[index].cat_id+'"><a href="'+data[index].url+'">'+data[index].cat_name+'</a></li>');
    	});
    });

    // add optional link to store home page at the top
    $('#categories_wrapper ul').prepend('<li><a href="'+'[[ebay_store_url]]'+'">Store Home</a></li>');

}

function loadjQuery() {
    var head    = document.getElementsByTagName("head")[0];
    var script  = document.createElement("script");
    script.type = "text/javascript";
    script.src  = "//cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.min.js";
    head.appendChild(script);
    waitUntiljQueryIsLoaded();
}

function waitUntiljQueryIsLoaded() {
    if ( typeof window.jQuery !== 'undefined' && window.jQuery ) {
        if (typeof jQueryLoaded == 'function') {
            jQueryLoaded();
        }
    } else {
        window.setTimeout( waitUntiljQueryIsLoaded, 100 );
    }
}

// payload - executed when jQuery has been loaded
function jQueryLoaded() {
    jQuery(document).ready(function(){
       
        // load categories
        loadDynamicCategories();
       
    });     
}

// init
loadjQuery();

</script>

used on http://docs.wplab.com/article/139-how-to-use-dynamic-categories-in-your-ebay-listing