␡
- 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
Using For/In Loops
(Netscape and Internet Explorer/Mac)
The previous example shows how to use JavaScript to write with a loop, but the way it's written demands that you know in advance the names of the objects you'll be displaying. Unfortunately, that's not always the case. In Script 3.4 , we use the for/in loop construction to display whatever the object's properties happen to be. The for/in loop checks for all the properties in a specified object.
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Script 3.4 This type of loop allows you to display objects when you don't even know what they are.
To use a for/in loop
- for (j in thisPlugin) { The variable thisPlugin, as in the previous example, is set to the current plug-in that we're processing. Instead of just writing out, for example, thisPlugin.filename, we instead use a for/in loop to look at every property that thisPlugin contains. Because i is already in use in the outer loop, we use our next choice of loop variable name, j. Each time we go around the loop, j will be set to the name of the next property of the thisPlugin object. It's important to note that j is not a number; unlike i, it's a string, even though it's a loop variable.
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document.write(j + ": " +
Inside the loop, we can use j (the name of the property) and thisPlugin[j] (the value of that property) to display all the properties of the user's plug-ins on our page. Figure 3.6 (Netscape/Win) and Figure 3.7 (Internet Explorer/Mac) show one of the main reasons why this functionality is so useful: the plugin object on each platform differs from the other. The former has item and namedItem properties that the latter doesn't, but this script happily displays both.
thisPlugin[j] + "<br \/>")
Figure 3.6 All the plug-ins and all their properties are shown in Netscape/Win.
Figure 3.7 The Internet Explorer/Mac plug-ins and properties are displayed, with some differences.
- } This closing brace ends the for/in loop.
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Tips
- It's important to note that, while these scripts are labeled as not working in Internet Explorer/Win, it's only the plug-in part of the code that's unsupported. Loops (of all sorts) work just fine in all browsers.