- Lesson 11: Prompts and Variables
- Lesson 12: Dates and Times
- Lesson 13: Hierarchy of Objects
- Lesson 14: Creating a Function
- Lesson 15: An Introduction to Arrays
- Lesson 16: The Third End-of-Chapter Review—A <BODY> Flag Script
This chapter is from the book
This chapter is from the book
This chapter is from the book
Lesson 16: The Third End-of-Chapter Review—A <BODY> Flag Script
If you stopped at this point, you would do just fine. What you have is sufficient to create some wonderful scripts.
But why stop now? Let's review!
Table 3.1 contains the object-related JavaScript commands you've learned up to now. In addition, you've been introduced to these JavaScript concepts:
The alert() method and the prompt() method
These event handlers: onBlur, onChange, onClick, onDblClick, onFocus, onKeyDown, onKeyPress, onKeyUp, onLoad, onMouseDown, onMouseMove, onMouseOut, onMouseOver, onMouseUp, onSubmit
The HTML 4.0 flag <SPAN>
Creating variable names
Creating a function
Table 3.1 Object-Related JavaScript Commands Demonstrated in Chapters 1–3
|
Object |
Methods |
Properties |
|
date |
getDate(), getDay(), getHours(), getMinutes(), getMonth(), getSeconds(), getYear() |
|
|
document |
write() |
alinkColor, bgColor, fgColor, linkColor, lastModified, location, referrer, title, vlinkColor |
|
history |
go() |
length |
|
location |
|
host, hostname, href |
|
navigator |
|
appCodeName, appName, appVersion, userAgent |
|
window |
|
defaultstatus, status |
Next, let's use some of these commands to create a script that helps the viewer create the page. The script will ask the viewer what background and text colors she would like. Then, the page will display with those colors. Finally, the viewer will be told, in the status bar, Here's your color background and color text.
The script is as follows:
<SCRIPT LANGUAGE="javascript">
var color = prompt("What color would you like the page's background to be","")
var txtcolor = prompt("What color would you like the text to be?","")
document.write("<BODY BGCOLOR=" +color+ " TEXT=" +txtcolor+ ">")
defaultStatus="Here's your " +color+ " background and " +txtcolor+ " text"
</SCRIPT>
Figure 3.8 shows the script's effect.
){kind=link}
Figure 3.8 The script creates a page with the user's desired background color and text color.
Click Here!
You can see this effect on your computer by clicking Lesson Sixteen Script's Effect, or see it online at http://www.htmlgoodies.com/JSBook/lesson16effect.html.
Deconstructing the Script
The script starts by setting a couple of variables using prompts. You need to get the user's input on what background and text color she wants, so this seems as good a way as any.
The variables are color and txtcolor, respectively. The code looks like this:
var color = prompt("What color would you like the page's background to be","")
var txtcolor = prompt("What color would you like the text to be?","")
Now that you have the input from the user, you'll need to use that data to alter the page. The real beauty of this script is its placement on the page.
Up until now, each of the scripts in this book had no real placement concerns. The script could pretty much sit anywhere in an HTML document, and the results would display. Now, though, you are concerned with where this script will place its output.
The script must write its line of text so that that line of text becomes the HTML document's <BODY> flag.
The quickest way to implement the user's background and text color requests is to write them to the <BODY> flag. So that's what you did. This script's main purpose is to write the HTML document's <BODY> flag to the page, so you must ensure that the entire script sits right where the body command needs to sit on the HTML page. And, of course, you need to ensure that you don't write a <BODY> into the HTML document yourself. You need to let the script do that for you.
Here's the code that writes the <BODY> flag:
document.write("<BODY BGCOLOR=" +color+ " TEXT=" +txtcolor+ ">")
The colors are entered as return variables inside the two plus signs. That way, what the user writes in the prompt is what is returned.
Status Bar, Too?
But the script goes a little further than just writing a <BODY> flag. It also places the viewer's data to the status bar, almost as if the page were served to her.
Here's the line of code that does it:
defaultStatus="Here's your " +color+ " background and " +txtcolor+ " text"
It follows the same format as the document.write statement, with text surrounded by double quotation marks and return variables surrounded by plus signs, except in this case the text is sent to the status bar.
Your Assignment
Okay, your turn. Make a new script—something that adds to your page. I stuck with prompts and variables for my example.
If you want to, may I suggest creating a Mad-Lib party game? It's that game where you're asked for a noun, a verb, a state, and things like that. Then, you read the sentence you created using those words. And you know from playing it that the sentence never makes any sense.
It would be your first JavaScript game.
For my brand-new script, I created a button that, when clicked, displays the current date and time. It's rather simple. (You should try the Mad-Lib game or something even more helpful.)
Click Here!
You can see a possible answer to making the button that shows the date and time by clicking Lesson Sixteen Assignment in your download packet, or see it online at http://www.htmlgoodies.com/JSBook/assignment16.html.