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Chapter 7

Real-Life Examples I


CONTENTS

This chapter includes several example JavaScript applications that apply the techniques you learned in Part II, "Using JavaScript Objects and Forms." These include the following:

  • Example 1: Displaying a Pop-Up Message: A page that includes an "instructions" link, which opens a small window to display the instructions.
  • Example 2: Displaying Random Quotations: An example of a method of displaying a different quotation each time the user loads the page.
  • Example 3: A Validated Registration Form: An example of a registration form for a commercial Web site, including validation for key fields.

Example 1: Displaying a Pop-Up Message

One thing lacking in HTML is a method of including pop-up messages. These messages appear in a small window and go away when you click on them or perform another action. This could be useful for a disclaimer, brief instructions, or anything you want to display to the user quickly without leaving the current page.

The following techniques are used in this example:

  • Defining and using a function (Chapter 3)
  • Using an event handler to trigger an action (Chapter 3)
  • Creating a new window and controlling its appearance (Chapter 5)
  • Using the window object's close() method (Chapters 3 and 5)

For this example, let's create a link to the word instructions on a Web page. Clicking this link will pop up a window with some brief instructions; you can then click a button in that window or move the focus to the main window, and the window will disappear.

You could create a simple pop-up message using a JavaScript alert, but this isn't perfect-for starters, it includes the nonfriendly message "JavaScript Alert:" at the top. It also uses plain text; your pop-up instructions can include boldface, italics, and anything else supported by HTML.

The main HTML document for the pop-up window example is Listing 7.1. This is the main page, and it includes a link to the word instructions to display the pop-up instructions.


Listing 7.1. (POPUP.asp) The main HTML document for the pop-up window example.
<HTML> <HEAD><TITLE>Pop-up Messages</TITLE> <SCRIPT LANGUAGE="JavaScript"> function instruct() { iwin = window.open("instruct.asp","IWIN", "status=no,toolbar=no,location=no,menu=no,width=400,height=300"); } </SCRIPT> </HEAD> <BODY> <H1>Pop-up Message Test</H1> <HR> This page demonstrates the use of a pop-up window. The window is created when the link below is clicked, and disappears when the OK button is pressed. <HR> Before you continue with this page, please take a quick look at the <A HREF="#" onClick="instruct();"> instructions</A>. <HR> The page continues... </BODY> </HTML>

The word instructions is a link. To avoid sending the user to an actual destination, this listing uses # as the link destination. The actual work for this link is done by the event handler, which calls the instruct() function.

The instruct() function is defined in the header. It includes the command to create the new window, specifying INSTRUCT.asp as the document to be loaded into the new window. The window attributes are set to turn off the status line, menu bar, toolbar, and other features, and set the window size.

The second HTML document, shown in Listing 7.2, is the document containing the actual instructions. This document also includes a bit of JavaScript-the OK button is defined with an event handler to close the window.


Listing 7.2. (INSTRUCT.asp) The second HTML document for the pop-up window example.
<HTML> <HEAD><TITLE>Instructions</TITLE> </HEAD> <BODY> <H1>Instructions</H1> These are the instructions. This is actually a separate HTML document, INSTRUCT.asp. This can include <b>bold</b>, <i>italic</i>, and other HTML features, since it's an ordinary HTML document. Click the button below to return. <FORM NAME="form1"> <INPUT TYPE="button" VALUE="OK" onClick="window.close();"> </FORM> </BODY> </HTML>

Figure 7.1 shows this example in action, with the instructions window displayed. Here are a few interesting observations about this example:

Figure 7.1 : The pop-up window example in action.

  • One potential problem could be caused if the user doesn't click on the OK button in the instructions window. The window will remain open. One solution is to use the onUnload event handler to close the instructions window when the main window closes.
  • Notice that although the new window you created is called iwin, it is referred to in INSTRUCT.asp as simply window. This is because for this document, the instructions window is the current window.
  • You have control over the appearance of the new window, but not complete control-for example, the title bar cannot be turned off. This is partially due to cross-platform issues; not all GUIs support a window with no title.

Example 2: Displaying Random Quotations

One of the things that keeps users coming back to a good Web page is variety-something different every time they visit. Using JavaScript, you can add a random quotation, a random link, or a random tip to the page.

For this example, let's display a random quotation at the top of a Web page. This example illustrates the following techniques:

  • Using the Math object's methods (Chapter 4)
  • Creating arrays and storing data (Chapter 4)
  • Creating HTML "on the fly" with the document.write method (Chapter 5)

You will embed the script to generate random quotations in the body of the Web page with the <SCRIPT> tag. Listing 7.3 is the HTML document, including the JavaScript program.

Note
This script uses the Math.random() method, which wasn't supported for all platforms until Netscape 3.0b3. Be sure you try it with the most recent version.


Listing 7.3. (RANDQUOT.asp) The HTML document for the random quotations example.
<HTML> <HEAD><TITLE>Random Quotations</TITLE> </HEAD> <BODY> <H1>Random Quotations</H1> <HR> <SCRIPT LANGUAGE="JavaScript"> //store the quotations in arrays quotes = new Array(6); authors = new Array(6); quotes[0] = "I have a new philosophy. I'm only going to dread one day at a time."; authors[0] = "Charles Schulz"; quotes[1] = "Reality is the leading cause of stress for those in touch with it."; authors[1] = "Jack Wagner"; quotes[2] = "Few things are harder to put up with than the annoyance of a good example."; authors[2] = "Mark Twain"; quotes[3] = "The pure and simple truth is rarely pure and never simple."; authors[3] = "Oscar Wilde"; quotes[4] = "There's no business like show business, but there are several businesses like accounting."; authors[4] = "David Letterman"; quotes[5] = "Man invented language to satisfy his deep need to complain."; authors[5] = "Lily Tomlin"; //calculate a random index index = Math.floor(Math.random() * quotes.length); //display the quotation document.write("<DL>\n"); document.write("<DT>" + "\"" + quotes[index] + "\"\n"); document.write("<DD>" + "- " + authors[index] + "\n"); document.write("</DL>\n"); //done </SCRIPT> <HR> The quotation above was generated randomly when you loaded this page. Reload for another one, or cheat-view the source code and see them all. <HR> </BODY> </HTML>

This example uses two arrays, quotes and authors, to store the quotations. Notice that an array can hold more than just numbers-in this case, each array element is a string.

To select a random quotation, you use Math.random() to produce a random number between 0 and 1. You then multiply it by the number of quotations, provided by the length property of the array, to produce a number in the right range. All this is enclosed in the Math.floor function, which removes the fractional part of the result.

Figure 7.2 shows the output of this example. Here are a few observations and notes about this program:

Figure 7.2 : The output of the random quotations example.

  • I've used this example to display a random humorous quotation. You could substitute tips about the current page, short advertisements about the company, or even random links-you can include HTML within the array elements without causing a problem.
  • There are only six quotations in this example-to keep things short. You could easily add more; just continue with quotes[6] and so on. Be aware that this is within the HTML source, though, so the more available quotes, the slower the user's access to the page. Just for fun, I've included a version of this program with over 100 quotations on the CD-ROM.
  • Notice that there are two arrays, one for quotations and one for authors. An object-oriented alternative is to create a new object with two string properties, then store an object in each array element. For example, you could create a Quotation object with author and quote properties. You might find this useful if you have more than two parts for each of your random items.

Example 3: A Validated Registration Form

Many Web pages-especially commercial ones, or services you pay for-include some sort of registration form so that users can submit information about themselves. For this example, let's create a registration form, including validation with JavaScript.

This example illustrates the following techniques:

  • Using string objects (Chapter 4)
  • Building and validating forms (Chapter 6)
  • Using the mailto: method to get results from a form without using CGI (Chapter 6)

As with the examples in Chapter 6 "Using Interactive Forms," you need to include the functions to validate the form in the header of the HTML document. The HTML source for the validated registration form is shown in Listing 7.4.


Listing 7.4. The HTML source code for the validated registration form.
<HTML> <HEAD><TITLE>Registration Form</TITLE> <SCRIPT> //global variable for error flag var errfound = false; //function to validate by length function ValidLength(item, len) { return (item.length >= len); } //function to validate an email address function ValidEmail(item) { if (!ValidLength(item, 5)) return false; if (item.indexOf ('@', 0) == -1) return false; return true; } // display an error alert function error(elem, text) { // abort if we already found an error if (errfound) return; window.alert(text); elem.select(); elem.focus(); errfound = true; } // main validation function function Validate() { errfound = false; if (!ValidLength(document.regform.username.value,6)) error(document.regform.username,"Invalid Name"); if (!ValidLength(document.regform.phone.value,10)) error(document.regform.phone,"Invalid phone number"); if (!ValidEmail(document.regform.email.value)) error(document.regform.email, "Invalid Email Address"); if (!ValidLength(document.regform.address.value,10)) error(document.regform.address, "Invalid Mailing Address"); if (!ValidLength(document.regform.city.value,15)) error(document.regform.city, "Invalid City/State/Zip"); return !errfound; /* true if there are no errors */ } </SCRIPT> </HEAD> <BODY> <H1>Registration Form</H1> <HR> Please fill out the fields below to register for our web page. Press the Submit button at the end of the form when done. <HR> <FORM NAME="regform" onSubmit="return Validate();" ACTION="mailto:username@host" METHOD="post"> <B>Your Name:</B> <INPUT TYPE="text" NAME="username" SIZE=20><BR> <B>Your Phone Number: </B> <INPUT TYPE="text" NAME="phone" SIZE=15><BR> <B>E-mail address:</B> <INPUT TYPE="text" NAME="email" SIZE=20><BR> <B>Mailing address:</B> <INPUT TYPE="text" NAME="address" SIZE=30><BR> <B>City, State, Zip:</B> <INPUT TYPE="text" NAME="city" SIZE=30> <HR> <INPUT TYPE="SUBMIT" NAME="submit" VALUE="Submit Registration"> <INPUT TYPE="RESET" VALUE="Start Over"> </FORM> </BODY> </HTML>

This application includes several functions:

  • Validate() validates the fields of the form and returns true or false depending on whether any errors were found. The user's name, phone number, e-mail address, and mailing address are all validated.
  • error() displays an appropriate error message when a field is invalid.
  • ValidLength() is used to verify that the text the user entered into a field is greater than a certain length. This is used for most of the fields.
  • ValidEmail() validates an e-mail address. It checks for a total length greater than five characters and makes sure an "at" sign (@) appears somewhere in the text.

Netscape's view of this form is shown in Figure 7.3. In the figure, an invalid e-mail address has been entered, and an alert is being displayed with the error message.

Figure 7.3 : The validated registration form in action.

The mailto: action is used to submit the data. (Be sure to replace user@host with your e-mail address.) If the user submits the form and validation is successful, a simple e-mail message is sent with the information from each of the fields. An example of such a message is shown in Listing 7.5.


Listing 7.5. The e-mail message sent as a result of the registration form.
username=Michael+Moncur&phone=555-555-2314 &email=guides@starlingtech.com &address=234+Elm+Street &city=Anywhere%2C+USA+44444 &submit=Submit+Registration

As you can see, this doesn't exactly come back in English. It's even worse than you think-I added the line breaks in the listing. Nevertheless, you can read the results. Software is also available to read it automatically.

The encoding in Listing 7.5 is called URL encoding and is used when data is sent to a CGI script. You'll look at this process in detail in Chapter 17, "Combining JavaScript, CGI, and SSI."







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