VBScript and JScript

Posted by arlene

Microsoft’s Internet Explorer browser supports VBScript, a variant of Visual Basic, as an alternative to JavaScript, which it also supports under the name of JScript. On Internet Explorer, VBScript and JScript are just syntactic alternatives, with the same functionality, but JScript and JavaScript differ in some areas of functionality, despite being broadly compatible.

Some users with Basic programming experience may find VBScript more palatable than JavaScript/JScript, which appeals more to programmers familiar with C or C++, but since VBScript only works with Internet Explorer which is not available on all platforms, it’s probably preferable to use JavaScript/JScript for the sake of full cross-platform and cross-browser portability, and test for compatibility with as many configurations as possible.

Recently, VBScript has given rise to widespread security worries owing to its ability to facilitate the spread of email worms and viruses, so many users may be disposed to disable it, and it may be unwise to assume its availability even on Windows machines.

Dynamic HTML

The original HTML specification was restricted in many ways, allowing only static, unchanging content with limited interactivity through the use of forms. While it was possible to display non-interactive animated graphics using the GIF89 standard, and even to create dynamically updated displays by use of frames coupled with JavaScript scripting, such expedients were quite limited in flexibility and required careful design.

However, recent browsers (Netscape 4, IE 4) support Dynamic HTML (DHTML), which allows a much greater degree of interactivity between the user/participant and the content of a web page. Much of the power of DHTML derives from the concept of a layer, a separately encapsulated block of HTML content that can be positioned absolutely on the page using co-ordinates, and with which JavaScript can interact. For example, a layer can be made visible or invisible in response to a mouse-click, or moved or resized dynamically by dragging the mouse pointer. This can be very useful for creating different types of interface device, such as buttons that display text when clicked (made by superimposing two layers, one on top of the other — when the topmost is clicked, it becomes invisible, revealing the one beneath). Such a device could be useful to create computer-based versions of paradigms in which cards are turned over, such as Wason’s Four-Card problem. Other useful trick is to create invisible layers at the beginning of the trial, which are revealed selectively to give feedback in response to user interaction.

Unfortunately, contemporary browsers use different standards for DHTML, so if you want your client system to work with both Netscape and Internet Explorer, you will have to write separate JavaScript and JScript sections to deal with both possibilities. And while Netscape supports a special <LAYER> tag to define layers, Internet Explorer does not. So, for maximum portability, to define a layer that will work in both types of browser, it is necessary to treat it as an absolutely positioned block of HTML content in Cascading Style Sheet (CSS) syntax, which is mostly portable between the browsers. Then you will need to write separate JavaScript and JScript handlers to deal with the remaining differences between them.

Example: A button-based interface using DHTML. The example given here shows an client that uses JavaScript and DHTML to implement a button-based interface for a decision-making task. Across a series of trials, participants learn to determine a town of origin of an imaginary person from a set of properties, which they may query by clicking on the buttons on the top row. When clicked, the buttons each reveal whether the imaginary person does or does not have the property; actually they are each composed of two layers, one above the other, and when the link on the top layer is clicked, it is made invisible, revealing the layer beneath. Participants select what they think is the town of origin by clicking on one of the buttons in the bottom row, which work the same way, but which also reveal the box in the centre when clicked. By using event capture, any click within a button’s boundary can be routed to the textual links on its top layer, and of course all click events can be timed and logged if desired.

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