␡
- Detecting Browser Plug-ins
- Around and Around with Loops
- Writing with Loops
- Using For/In Loops
- Using Do/While Loops
- Checking if Java Is Enabled
- Functions
- Using Multi-level Conditionals
- Working with Functions That Return Values
- Handling Errors
- Putting More than One Script on a Page
- Scrolling Status Bars
- Status Bar Messages
This chapter is from the book
This chapter is from the book
This chapter is from the book
This chapter is from the book
Writing with Loops
(Netscape and Internet Explorer/Mac)
Sometimes you'll want to get information out of JavaScript objects and display them to the user. Using JavaScript to write the user's Web page on the fly is a useful technique, one you'll find yourself using often. In this example ( Script 3.3 ), you'll use a loop to display all of the plug-ins installed in your browser, and write a list of them out to the browser window.
)
Script 3.3 You can use loops to step through JavaScript objects and write to the browser window.
To write a Web page using a loop
-
if (navigator.plugins && navigator.
If both of these values are true, continue on with the following code.
plugins.length > 0) {
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document.write("You have theThe information on the page will be displayed inside a table, so we'll start it off by writing out the <table> tag here. following plugins: <table
cellspacing='4' cellpadding='4'>")
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document.write("<tr><th bgcolor=This line of code writes out the headers for the first row of the table. '#CCCCCC'>Name<\/th><th bgcolor=
'#CCCCCC'>Filename<\/th><th bgcolor=
'#CCCCCC'>Description<\/th><\/tr>")
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for (i=0; i<navigator.plugins.length;
This line, as in the previous example, loops through each installed plug-in. i++) {
- thisPlugin = navigator.plugins[i] Rather than refer to each plug-in by its full name, we set up a temporary variable that saves the value of the plug-in that we're currently interested in.
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document.write("<tr valign='top'>This line starts a new row and cell, and writes out the name of the current plug-in. <td bgcolor='#CCCCCC'>" +
thisPlugin.name)
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document.write("<\/td><td bgcolor=The old table cell is ended, a new one begins, and the filename of the plug-in is written to the page. '#CCCCCC'>" + thisPlugin.filename)
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document.write("<\/td><td bgcolor=Another cell ends, a new one begins, and the description of the plug-in finishes off the cell and row. '#CCCCCC'>" + thisPlugin.
description + "<\/td><\/tr>")
- } This brace ends the loop, and the lines inside are repeated for each plug-in installed in the user's browser.
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document.write("<\/table>")
When the loop has finished, we write out the ending <table> tag to finish off the code, as shown in
Figure 3.5
.
Figure 3.5 This table of plug-ins was written to the browser window using a loop.
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document.write("JavaScript couldn'tIf the user has a browser that doesn't support viewing the plug-ins through JavaScript, this is the message they'll see. find any plugins")
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Tip
- You can have more than one check inside an if statement just by putting both checks inside the parentheses that follow the if. Using the double ampersand between the two means that both values must be true in order to execute the following lines of code.