Home > Articles > Open Source > Ajax & JavaScript

  • Print
  • + Share This
This chapter is from the book

Functions

Functions in any programming language are ways to write code that can be used later. At its most basic form, this is also true for JavaScript. You can write a chunk of custom code and not only execute it at will, but you can also execute it over and over, which can help streamline your application by increasing its maintainability (declaring a chunk of code one time and referencing it, rather than rewriting what it does). It’s like keeping all your CSS in the same file or why you keep all JavaScript in the same file—you know exactly where it is when you need to change or add something.

You’ve been using functions already in earlier chapters when you pass data into an alert(). “Alert” is technically called a method but for all intents and purposes, it’s the same as a function.

Basic Functions

The chance of creating a JavaScript application without having to write your own functions is pretty low. It’s something that you’ll be doing on every project, and it’s very easy to do using the function keyword (remember the reserved words list? This is what function is for).

Using the function keyword is like saying, “Hey, I’m building something over here that should be treated as a function.” Listing 6.2 shows a basic function declaration.

Listing 6.2. Writing a Basic Function

function sayHello() {

    alert("hey there! ");

}

Calling a Function

Calling a function is very simple. You type out the name, and then parentheses and the function will be executed. The parentheses tell the browser that you want to execute the function and to use any data (arguments) contained within the parentheses within the function. Listing 6.2.1 shows how to call the function we declared in Listing 6.2. It should alert the text, “hey there!”

Listing 6.2.1. Calling a Basic Function

sayHello(); // hey there

Arguments

Arguments are a way to pass information or data into a function. As previously mentioned, up to this point you’ve been using the alert() method. We’ve also been passing it arguments. The alert method is designed in native JavaScript to take arguments and display them in the form of a pop-up box in the browser.

Functions can take any number of arguments. They can be any type of information; strings, variables, large data sets, and anything else you can think of can be passed into a function through an argument. As you’re defining your functions, you will be assigning names to the arguments, sort of like the way you assign names to a variable. After that argument is named in the function, it becomes a variable you’ll be using inside that function.

In Listing 6.2.2 you can see that the sayHello() function now has a single argument called “message.” Inside, the function “message” is used as a variable that gets passed into the JavaScript alert() method.

Listing 6.2.2. Passing a Function Variable Through Arguments

/* declare the function */
function sayHello(message){

    alert(message); // "message" is also an argument in the "alert" method

}

/* call it a couple times with different messages */
sayHello("Hey there, you stink!");

sayHello("I feel bad I just said that.");

When this function is called, we’re setting the string argument to “Hey there, you stink!” and then quickly apologizing with another alert, because frankly it was kind of rude. This is a very real-life way arguments are used in functions. The string can either be declared upon calling the function (like we’re doing in Listing 6.2.2) or it can be declared immediately in the function declaration. (Instead of using the message variable, you could insert the string.) Calling it the way we did is much more common in the real world, though.

Anonymous Functions

Anonymous functions are functions that have no name (obviously—they’re anonymous). They execute immediately and can contain any number of other functions. The syntax for declaring an anonymous function is a little different. They are dynamic in nature because they are executed at runtime rather than waiting to be called.

Anonymous functions perform very well in the browser because there is no reference to them in another part of the document. This comes with pluses and minuses. So as you write your JavaScript, it is always good to note that if you have to rewrite an anonymous function over and over, it’s probably best to pull it out into a normal function to cut down on maintenance and repetitive code.

There is often a little confusion as to the purpose of anonymous functions. If you want something to execute at runtime, why wouldn’t you just dump the code right into your JavaScript file? Why even bother wrapping it in an anonymous function? Well, this is a good place to bring up a term you may hear a lot: scope.

  • + Share This
  • 🔖 Save To Your Account

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT 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 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 information@informit.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 InformIT. 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.informit.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