在纯Javascript中执行简单的Parent-Child下拉菜单的最佳方法是什么

I need to do a quick and dirty 'Country' --> 'State' drop down relationship on a web form. I only am concerned with the states, provinces, and territories for USA and Canada, and this will be a relatively lightly used form, so a pure javascript solution is probably ideal.I need to do a quick and dirty 'Country' --> 'S