Allow only alphanumeric characters in text input field with Jquery

gistfile1.txt

$(function() {

  $('#sidebar-filters-submit').click(function(e) {
    $(".navigation").find(".error").remove();
    allOk = true;

    if ($("#search_page_keywords").val()) {
      var input = $("#search_page_keywords").val();
      if (/^[a-zA-Z0-9 ]*$/.test(input) === false) {
        $("<label for=\"search_keyword_input\" class=\"search_keyword_input error\"> Your search string contains illegal characters.</label>").insertAfter("#search_page_keywords");
        allOk = false;
      }
      if (!allOk) {
        e.preventDefault();
      }
    }

  });
});