如何用JavaScript加载外部文件?

I am writing a script where you can add and remove a drop-down list of languages. I got it working but my question is if there is a way to externalize the select tag part of the code as I would have more than 100 options and load it in JavaScript when a link is click. I don't want to have 100 option tags within the script. On the PHP side I use the the include statement to load my list of options.I am writing a script where you can add and rem