哪种技术用于动态更新组合框内的值？

I'm making a webpage and in it the values inside the combo box depends upon the selection of some other field like for registration form by selecting a specific country, the combo box for the states displays the states of only that country. So does this dynamic allocation of values to the combo box occurs with javascript or with some back-end programming language like java or C++? If it can occur through both than which would be more advisable to use? Thanks in advance.I'm making a webpage and in it the values insid