VBScript was initially intended for client-side scripting. It provided a Visual Basic-like method for HTML developers to add interactivity to their web pages. The hope was that since many developers were familiar with Visual Basic, a scripting language modeled after the application development tool would have a wide audience. The basic concept proved to be correct, although client-side scripting with VBScript never achieved the popularity its developers had hoped for. This is because client-side scripting with VBScript has a major downside: VBScript is supported only in Internet Explorer. This means that you have to either force your users to a specific browser (which is really only possible on intranets), or script with both VBScript and some flavor of ECMAScript to make sure that you are providing the same functionality to all users. This, however, does not mean that scripting in ECMAScript will answer all of your compatibility issues, either.Netscape Navigator and Internet Explorer each have their own flavor of ECMAScript, which, while mostly similar, still have their differences. Anyway, we'll assume that if you are reading this chapter that you are interested in client-side scripting in Internet Explorer.