Publishers of technology books, eBooks, and videos for creative people

Home > Articles > Web Design & Development > PHP/MySQL/Scripting

JavaScript Language Essentials

  • Print
  • + Share This
Tom Negrino and Dori Smith go into detail about the basic elements of JavaScript and introduce you to other aspects of the JavaScript language, such as loops, arrays, and more about functions.
This chapter is from the book

Now that you've gotten your feet wet, let's wade a bit deeper into the JavaScript language. In this chapter, we'll go into more detail about the basic elements of JavaScript and introduce you to other aspects of the JavaScript language, such as loops, arrays, and more about functions (don't let your eyes glaze over; we promise that it'll be easy).

You'll see how you can use JavaScript to write your Web pages for you, learn how JavaScript handles errors that the user makes, and much more.

Table 3.1. Just Enough HTML—The Basics

Tag

Meaning

table

Presents tabular data on a Web page

tr

Begins a row inside the table

th

Heading cells for the columns in the table

td

Contains each cell in the table

Around and Around with Loops

It's common in programming to test for a particular condition and repeat the test as many times as needed. Let's use an example you probably know well: doing a search and replace in a word processor. You search for one bit of text, change it to a different text string, and then repeat the process for all of the instances of the first string in the document. Now imagine that you got a program to do it for you automatically. The program would execute a loop, which lets it repeat an action a specified number of times. In JavaScript, loops become a vital part of your scripting toolbox.

More about loops

The kind of loop that we mostly use in this book is the for loop, named after the command that begins the loop. This sort of loop uses a counter, which is a variable that begins with one value (usually 0) and ends when a conditional test inside the loop is satisfied.

The command that starts the loop structure is immediately followed by parentheses. Inside the parentheses you'll usually find the counter definition and the way the counter is incremented (i.e., the way the counter's value is increased).

In the next several examples we're going to build a simple yet familiar application, a Bingo card. We'll use each example to show you a new aspect of JavaScript. We'll begin with an HTML page, Script 3.1. It contains the table that is the Bingo card's framework (Figure 3.1). Take a look at the script, and you'll see that the first row contains the letters at the top of the card, and each subsequent row contains five table cells. Most cells contain just a non-breaking space (using the HTML entity  ); however, the third row contains the Free space, so one table cell in that row contains the word "Free". Note that each cell has an id attribute, which the script uses to manipulate the cell contents. The id is in the form of square0, square1, square2, through square23, for reasons that we'll explain below. At the bottom of the page, there's a link that generates a new card.

Script 3.1. This HTML page creates the skeleton for the Bingo card.

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
     <title>Make Your Own Bingo Card</title>
     <link rel="stylesheet" rev="stylesheet" href="script01.css" />
     <script src="script01.js" type="text/javascript" language="javascript"></script>
</head>
<body>
<h1>Create A Bingo Card</h1>
<table>
     <tr>
        <th width="20%">B</th>
        <th width="20%">I</th>
        <th width="20%">N</th>
        <th width="20%">G</th>
        <th width="20%">O</th>
     </tr>
     <tr>
        <td id="square0">&nbsp;</td>
        <td id="square1">&nbsp;</td>
        <td id="square2">&nbsp;</td>
        <td id="square3">&nbsp;</td>
        <td id="square4">&nbsp;</td>
     </tr>
     <tr>
        <td id="square5">&nbsp;</td>
        <td id="square6">&nbsp;</td>
        <td id="square7">&nbsp;</td>
        <td id="square8">&nbsp;</td>
        <td id="square9">&nbsp;</td>
     </tr>
     <tr>
        <td id="square10">&nbsp;</td>
        <td id="square11">&nbsp;</td>
        <td id="free">Free</td>
        <td id="square12">&nbsp;</td>
        <td id="square13">&nbsp;</td>
     </tr>
     <tr>
        <td id="square14">&nbsp;</td>
        <td id="square15">&nbsp;</td>
        <td id="square16">&nbsp;</td>
        <td id="square17">&nbsp;</td>
        <td id="square18">&nbsp;</td>
     </tr>
     <tr>
        <td id="square19">&nbsp;</td>
        <td id="square20">&nbsp;</td>
        <td id="square21">&nbsp;</td>
        <td id="square22">&nbsp;</td>
        <td id="square23">&nbsp;</td>
     </tr>
</table>
<p><a href="script01.html" id="reload"> Click here</a> to create a new card</p>
</body>
</html>
Figure 3.1

Figure 3.1 This Bingo card has randomly generated numbers, but it isn't a valid Bingo card. Yet.

Script 3.2 is the CSS file that we're using to style the contents of the Bingo card. If you don't know CSS, don't worry about it; we'll explain it in more detail in Chapter 11, and it doesn't matter much here anyway. The HTML and CSS pages won't change for the rest of the Bingo card examples, so we're only going to print them once here.

Script 3.2. This CSS file adds style to the Bingo card.

body {
     background-color: white;
     color: black;
     font-size: 20px;
     font-family: "Lucida Grande", Verdana, Arial, Helvetica, sans-serif;
}
h1, th {
     font-family: Georgia, "Times New Roman", Times, serif;
}

h1 {
     font-size: 28px;
}

table {
     border-collapse: collapse;
}

th, td {
     padding: 10px;
     border: 2px #666 solid;
     text-align: center;
     font-size: 24px;
}

#free {
     background-color: #F66;
}

This example shows you how to set up and use a loop to populate the contents of the Bingo card with randomly generated numbers. Script 3.3 contains the JavaScript you need to make it happen. The card that is generated from this script is not a valid Bingo card, because there are constraints on which numbers can be in particular columns. Later examples add to the script until the resulting Bingo card is valid.

Script 3.3. Welcome to your first JavaScript loop.

window.onload = newCard;

function newCard() {
     for (var i=0; i<24; i++) {
        var newNum = Math.floor(Math.random() * 75) + 1;

        document.getElementById("square"  + i).innerHTML = newNum;
     }
}

To use a loop to create the table's contents:

  1. window.onload = newCard;
    
    This is in Script 3.3. This line calls the newCard() function when the window finishes loading. It's common to use an event handler to call a function.
  2. function newCard() {
    
    This line begins the function.
  3. for (var i=0; i<24; i++) {
    
    This line begins the loop. Programmers traditionally use the variable i to denote a variable used as a counter inside a loop. First i is set to 0. A semicolon signals the end of that statement and allows us to put another statement on the same line. The next part is read as "if i is less than 24, do the following code inside the braces." The final bit (after the second semicolon) adds 1 to the value of i. Because this is new, let's break that down a bit. The i++ part uses the ++ operator you saw in Chapter 1 to increment the value of i by 1. The loop will repeat 24 times, and the code inside the loop will execute 24 times. On the first go-through, i will be 0, and on the last go-through i will be 23.
  4. var newNum = Math.floor (Math.random() * 75) + 1;
    Inside the loop, we create a new variable, newNum, and fill it with the result of the calculation on the right side of the parentheses. The built-in JavaScript command Math.random() gives us a number between 0 and 1, such as 0.123456789. Multiplying Math.random() by the maximum value (remember, values in Bingo cards can be from 1 to 75) gives us a result between 0 and one less than the max value. The floor of that result gives us the integer portion, i.e., an integer between 0 and (max value -1). Add one, and we have a number between 1 and our maximum value.
  5. document.getElementById ("square" + i).innerHTML = newNum;
    This is where we write into the table the value of the random number we just got. We get the element with the id named square with the current value of i concatenated onto it. For example, the first time through the loop, the value of i will be zero, so the line gets the element with the id of square0. Then the line sets the innerHTML property of the square0 object to the current value of newNum. Then, because we're still inside the loop, steps 4 and 5 happen again, until the whole Bingo card is filled out.
  • + Share This
  • 🔖 Save To Your Account

Peachpit Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from Peachpit and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about Peachpit products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites; develop new products and services; conduct educational research; and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email ask@peachpit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by Adobe Press. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.peachpit.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020