stuartelmore

Using jQuery:

$(document).ready(function(){
  $('#metakeyselect').change(function(){
    if($(this).val() == 'date'){
      $('#metakeyinput').addClass('date-calendar'); // adds class
    }else{
      $('#metakeyinput').removeClass('date-calendar'); // removes class if it already exists, otherwise will carry on.
    }
  });
});

can do a vanilla JavaScript if needed?