JavaScript and Ajax for the Web: Visual QuickStart Guide, Seventh Edition

Changing Menus Dynamically

It’s often useful to offer the user a choice of inputs via pop-up menus, and to be able to change the contents of one or more pop-up menus depending on the choice the user makes in another pop-up menu. You’ve probably seen this on Web sites that ask you to choose the country you live in from a pop-up menu and then fill a second menu with state or province names, based on the choice you made. In Scripts 7.3 (HTML) and 7.4 (JavaScript), we’re using two pop-up menus (Figure 7.3). The first menu is for months. When the user picks a month, the script populates the second pop-up menu with the correct number of days for the selected month (Figure 7.4).

Figure 7.3. The contents of the second menu are filled in automatically ...