Part 11: Working Directly with Code in Visual C#

Paint Quick Response Code in Visual C# Part 11: Working Directly with Code

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Events on the page can also trigger script code. There s an onClick event, for example, that occurs when the Web visitor clicks a button. If the Web page creator supplied code for that event, the code executes whenever the visitor clicks that button. Support for browser scripts varies widely. Some browsers support no scripting at all, some support only JavaScript, and some support both JavaScript and VBScript. In addition, the level of support varies with the browser version. Even among browsers that do support scripting, most provide a way for Web visitors to turn scripting off.

Working with Script Code If you decide to use scripting on a Web page, be sure to:

Test the script with all common browsers. Note (perhaps at the bottom of the page) the minimum browser version the visitor

Because JavaScript is the only scripting language Internet Explorer and Netscape Navigator have in common, it s the predominant language for browser-side scripting. JavaScript is the default scripting language for both browsers (that is, <script> defaults to <script language="JavaScript">). Note All recent versions of Internet Explorer and Netscape Navigator support some level of scripting. Browsers with no scripting support at all are generally very old or experimental. Browsers that don t support scripting easily ignore <script> and </script> tags, but what of the code between them An older browser can easily ignore unknown tags, but it has no reason to ignore content between unknown start and end tags. In the case of <script> tags, the old browser will generally try to interpret the script code as HTML, and this can get ugly fast. To prevent this, experienced coders often enclose script code in HTML comments, as shown here:

<!--

alert("Your message could appear here.");

The <!-- and --> tags mark the beginning and end of an HTML comment. Script languages successfully ignore the start <!-- tag, but the end --> tag presents a problem: a double minus sign is a valid JavaScript operator. Prefixing the closing tag with a double slash (//) marks it as a JavaScript comment as well as an HTML comment.

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The section Validating Form Input, in 34, has already described one method of generating browser scripts. Establishing validation rules for form elements generates script routines that the browser runs when the Web visitor clicks the form s Submit button. If the script detects no form element fields having values outside the prescribed range, it submits the form normally. If the script detects an incorrect value, it displays an error message to the visitor and submits nothing. The features on the DHTML Effects toolbar and those in the Behaviors task pane also generate JavaScript code that runs on the browser. Both of these features modify the browser display in response to visitor actions.

For more information about using the DHTML Effects toolbar, refer to Using DHTML Effects, on page 690. For more information about scripting page element behaviors, refer to Scripting DHTML Behaviors, on page 694.

If any of these facilities meet you needs, you should by all means use them. However, don t expect FrontPage to generate code you can customize. The JavaScript code that FrontPage creates is strictly for machine consumption.

Displaying Current Information (Coding Example 1)

Figure 41-1 showed a script that obtains and displays real-time information each time a Web visitor loads a page. Figure 41-2 shows the same page in preview mode. Note Preview mode displays the current Web page using whatever version of Internet Explorer is installed on your system.

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Figure 41-2. Here, in preview mode, FrontPage runs the script shown in Figure 41-1.

Of course, the information available to a script isn t limited to Date Last Modified. Figure 41-3 shows a Web page displaying a selection of more useful information. Each property value displayed in Figure 41-3 comes from a one-line script such as the following: