Search and replace specific query string parameter value in javascript

Based on this discussion I have created a references function. enjoy

updateUrlParameter(url, param, value){
    var regex = new RegExp("/([?|&]" + param + "=)[^\&]+/");
    return url.replace(regex, '$1' + value);
}

a_href = a_href.replace(/(test_ref=)[^\&]+/, '$1' + updated_test_ref);

Based on this discussion I have fixed the Chris function (problem with regex string!)

function updateUrlParameter(url, param, value){
    var regex = new RegExp('('+param+'=)[^\&]+');
    return url.replace( regex , '$1' + value);
}