Click here to close now.




















Welcome!

Apache Authors: Liz McMillan, Mohamed El-Refaey, Ajay Budhraja, Don MacVittie, AppDynamics Blog

Related Topics: Java IoT, Microservices Expo, IBM Cloud, Weblogic, IoT User Interface, Apache

Java IoT: Article

Book Excerpt: jQuery Essentials | Part 1

An introduction to jQuery

The basics of jQuery programming
In the next three figures, you're going to learn the basics of jQuery programming. Then, you'll study an application that uses these skills. That will show you how jQuery simplifies JavaScript programming.

How to code jQuery selectors
When you use jQuery, you start by selecting the element or elements that you want to apply a jQuery method to. To do that, you can use jQuery selectors as shown in Figure 4.

The syntax for a jQuery selector

$("selector")

The HTML for the elements that are selected by the examples

<section id="faqs">
<h1>jQuery FAQs</h1>
<h2 class="plus">What is jQuery?</h2>
<div>
<p>jQuery is a library of the JavaScript functions that you're most
likely to need as you develop web sites.
</p>
</div>
<h2 class="plus">Why is jQuery becoming so popular?</h2>
<div>
<p>Three reasons:</p>
<ul>
<li>It's free.</li>
<li>It lets you get more done in less time.</li>
<li>All of its functions cross-browser compatible.</li>
</ul>
</div>
</section>

How to select elements by element, id, and class

  • By element type: All <p> elements in the entire document
    $("p")
  • By id: The element with "faqs" as its id
    $("#faqs")
  • By class: All elements with "plus" as a class
    $(".plus")

How to select elements by relationship

  • Descendants: All <p> elements that are descendants of the section element
    $("#faqs p");
  • Adjacent siblings: All div elements that are adjacent siblings of h2 elements
    $("h2 + div")
  • General siblings: All <p> elements that are siblings of ul elements
    $("ul ~ p")
  • Children: All ul elements that are children of div elements
    $("div > ul")

How to code multiple selectors

$("#faqs li, div p")
$("p + ul, div ~ p")

Description
When you use jQuery, the dollar sign ($) is used to refer to the jQuery library. Then, you can code selectors by using the CSS syntax within quotation marks within parentheses.

Figure 4: How to code jQuery selectors

To code a jQuery selector, you start by coding the dollar sign ($) followed by set of parentheses that contains a set of quotation marks. Then, within the quotation marks, you code the CSS selector for the element or elements that you want to select. This is shown by the syntax summary at the top of this figure.

The HTML and the examples that follow show how easy it is to select one or more elements with jQuery. For instance, the first selector in the first group of examples selects all <p> elements within the entire document. The second selector selects the element with "faqs" as its id. And the third selector selects all elements with "plus" as the value of its class attribute.

In the second group of examples, you can see how other types of CSS selectors are coded with jQuery. Here, you can see how descendants, adjacent siblings, general siblings, and children are coded. For instance, the first selector gets all <p> elements that are descendants of the element with "faqs" as its id. That includes all of the <p> elements in the HTML in this figure.

In contrast, the second selector gets the div elements that are adjacent siblings to the h2 elements, which includes all of the div elements. The third selector gets all <p> elements that are siblings of ul elements, which selects the one <p> element in the second div element. And the fourth selector gets all ul elements that are children of div elements, which selects the ul element in the second div element.

The third group of examples shows how to code multiple selectors. To do that, you separate them with commas, just as you do with CSS.

How to call jQuery methods
Once you've selected the element or elements that you want to apply a method to, you call the method using the syntax shown at the top of Figure 5. This is the same way that you call a method of any object. You code the selector that gets the element or elements, the dot, the method name, and any parameters within parentheses.

The syntax for calling a jQuery method

$("selector").methodName(parameters)

Some common jQuery methods

Method

Description

val()

Get the value of a text box or other form control.

val(value)

Set the value of a text box or other form control.

text()

Get the text of an element.

text(value)

Set the text of an element.

next([type])

Get the next sibling of an element or the next sibling of a specified type if the parameter is coded.

submit()

Submit the selected form.

focus()

Move the focus to the selected form control or link.

Examples

How to get the value from a text box

var gallons = $("#gallons").val();

How to set the value for an input element

$("#gallons").val("");

How to set the text in an element

$("#email_address_error").text("Email address is required");

How to set the text for the next sibling with object chaining

$("#last_name").next().text("Last name is required");

How to submit a form

$("#join_list").submit();

How to move the focus to a form control or link

$("#email_address").focus();

Description

ŸTo call a jQuery method, you code a selector, the dot operator, the method name, and any parameters within parentheses. Then, that method is applied to the element or elements that are selected by the selector.

When you use object chaining with jQuery, you code one method after the other. This works because each method returns the appropriate object.

ŸIf the selector for a method selects more than one element, jQuery applies the method to all of the elements so you don't have to code a loop to do that.

Figure 5: How to call jQuery methods

To get you started with jQuery, the table in this figure summarizes some of the jQuery methods that you'll use the most. For instance, the val method without a parameter gets the value from a selected text box or other form control, and the val method with a parameter sets the value in a selected text box or other form control. The first two examples after the table show how this works.

Similarly, the text method without a parameter can be used to get the text of a selected element, and the text method with a parameter can be used to set the text of a selected element. Methods like these are often referred to as getter and setter methods. Here, third example illustrates the setter version of the text method, which sets the text of an element to "Email address is required".

The fifth method in the table is the next method, which is used to get the next (or adjacent) sibling of an element. This method is often followed by another method. To do that, you use object chaining, which works just as it does with JavaScript. This is illustrated by the fourth example. Here, the next method gets the next sibling after the element that has been selected, and the text method sets the text for that sibling.

The last two methods in the table are the submit and focus methods, which are just like the JavaScript submit and focus methods. The submit method submits the data for a selected form to the server, and the focus method moves the focus to the selected form control or link.

In a moment, you'll see how these selectors and methods work in an application. But first, you need to learn how to set up the event handlers for an application.

How to use jQuery event methods
When you use jQuery, you use event methods to attach event handlers to events. To do that, you use the syntax shown at the top of Figure 6. First, you code the selector for the element that will initiate the event like a button that will be clicked. Then, you code the name of the event method that represents the event that you want to use. Last, you code a function that will be the event handler for the event within parentheses.

The syntax for a jQuery event method

$(selector).eventMethodName(function() {
// the statements of the event handler
});

Two common jQuery event methods

Event method

Description

ready(handler)

The event handler runs when the DOM is ready.

click(handler)

The event handler runs when the selected element is clicked.

Two ways to code an event handler for the jQuery ready event

The long way

$(document).ready(function() {
alert("The DOM is ready");
});

The short way

$(function(){                // (document).ready is assumed
alert("The DOM is ready");
});

An event handler for the click event of all h2 elements

$("h2").click(function() {
alert("This heading has been clicked");
});

The click event handler within the ready event handler

$(document).ready(function() {
$("h2").click(function() {
alert("This heading has been clicked");
}); // end of click event handler
}); // end of ready event handler

Description

  • To code a jQuery event handler, you code a selector, the dot operator, the name of the jQuery event method, and an anonymous function that handles the event within parentheses.
  • The event handler for the ready event will run any methods that it contains as soon as the DOM is ready, even if the browser is loading images and other content for the page. This works better than the JavaScript onload event, which doesn't occur until all of the content for the page is loaded.
  • In this book, the ready event is always coded the long way that's shown above. In practice, though, many programmers use the short way.
  • When coding one event handler within another, the use of the closing braces, parentheses, and semicolons is critical. To help get this right, many programmers code inline comments after these punctuation marks to identify the ends of the handlers.

Figure 6: How to use jQuery event methods

In the table in this figure, the two event methods that you'll use the most are summarized. The ready event is the jQuery alternative to the JavaScript load event, except that it works better. Unlike the load event, the ready event is triggered as soon as the DOM is built, even if other elements like images are still being loaded into the browser. This means that the user can start using the web page faster.

Because the DOM usually has to be built before you can use JavaScript or jQuery, you'll probably use the ready event method in every JavaScript application that you develop. The examples in this figure show two ways to do that. In the long form, you use document as the selector for the web page followed by the dot, the method name (ready), and the function for the event handler.

In the short form, you can omit the selector and event method name and just code the function in parentheses after the dollar sign. Although this form is often used by professional developers, all of the examples in this book use the long form. That way, it's clear where the ready event handler starts.

The next example in this figure shows an event handler for the click event of all h2 elements. This is coded just like the event handler for the ready event except h2 is used as the selector and click is used as the name of the event method.

The last example in this figure shows how you code an event handler within the ready event handler. Note here that the closing brace, parenthesis, and semicolon for each event handler is critical. As you can guess, it's easy to omit one of these marks or get them out of sequence so this is a frequent source of errors. That's why professional programmers often code inline comments after the ending marks for each event handler to identify which event handler the marks are for.

More Stories By Mike Murach

As a freelance writer many years ago, Mike Murach decided that he had to develop his own writing methods because the ones that others were using clearly didn’t work. Since then, Mike and his staff have continued to refine those methods, so today every Murach book becomes the best one on its subject. Now, after a long hiatus from writing, Mike has teamed with Zak Ruvalcaba to write Murach’s JavaScript and jQuery.

More Stories By Zak Ruvalcaba

Zak Ruvalcaba has been researching, designing, and developing for the Web since 1995. He holds a BS from San Diego State University and an MS in instructional technology from National University in San Diego.

Zak's skillset includes HTML/HTML5, CSS/CSS3, JavaScript, jQuery, ASP.NET, ADO.NET, Visual Basic, C#, Web Services, and Flash/ActionScript. He is also a Microsoft Certified Application Developer for .NET (MCAD) and a Microsoft Certified Solutions Developer for .NET (MCSD).

In his spare time, Zak teaches web development courses for the San Diego Community College District, Mt. San Jacinto Community College and Palomar Community College.

Comments (0)

Share your thoughts on this story.

Add your comment
You must be signed in to add a comment. Sign-in | Register

In accordance with our Comment Policy, we encourage comments that are on topic, relevant and to-the-point. We will remove comments that include profanity, personal attacks, racial slurs, threats of violence, or other inappropriate material that violates our Terms and Conditions, and will block users who make repeated violations. We ask all readers to expect diversity of opinion and to treat one another with dignity and respect.


@ThingsExpo Stories
SYS-CON Events announced today that HPM Networks will exhibit at the 17th International Cloud Expo®, which will take place on November 3–5, 2015, at the Santa Clara Convention Center in Santa Clara, CA. For 20 years, HPM Networks has been integrating technology solutions that solve complex business challenges. HPM Networks has designed solutions for both SMB and enterprise customers throughout the San Francisco Bay Area.
For IoT to grow as quickly as analyst firms’ project, a lot is going to fall on developers to quickly bring applications to market. But the lack of a standard development platform threatens to slow growth and make application development more time consuming and costly, much like we’ve seen in the mobile space. In his session at @ThingsExpo, Mike Weiner, Product Manager of the Omega DevCloud with KORE Telematics Inc., discussed the evolving requirements for developers as IoT matures and conducted a live demonstration of how quickly application development can happen when the need to comply wit...
The Internet of Everything (IoE) brings together people, process, data and things to make networked connections more relevant and valuable than ever before – transforming information into knowledge and knowledge into wisdom. IoE creates new capabilities, richer experiences, and unprecedented opportunities to improve business and government operations, decision making and mission support capabilities.
Explosive growth in connected devices. Enormous amounts of data for collection and analysis. Critical use of data for split-second decision making and actionable information. All three are factors in making the Internet of Things a reality. Yet, any one factor would have an IT organization pondering its infrastructure strategy. How should your organization enhance its IT framework to enable an Internet of Things implementation? In his session at @ThingsExpo, James Kirkland, Red Hat's Chief Architect for the Internet of Things and Intelligent Systems, described how to revolutionize your archit...
MuleSoft has announced the findings of its 2015 Connectivity Benchmark Report on the adoption and business impact of APIs. The findings suggest traditional businesses are quickly evolving into "composable enterprises" built out of hundreds of connected software services, applications and devices. Most are embracing the Internet of Things (IoT) and microservices technologies like Docker. A majority are integrating wearables, like smart watches, and more than half plan to generate revenue with APIs within the next year.
Growth hacking is common for startups to make unheard-of progress in building their business. Career Hacks can help Geek Girls and those who support them (yes, that's you too, Dad!) to excel in this typically male-dominated world. Get ready to learn the facts: Is there a bias against women in the tech / developer communities? Why are women 50% of the workforce, but hold only 24% of the STEM or IT positions? Some beginnings of what to do about it! In her Opening Keynote at 16th Cloud Expo, Sandy Carter, IBM General Manager Cloud Ecosystem and Developers, and a Social Business Evangelist, d...
In his keynote at 16th Cloud Expo, Rodney Rogers, CEO of Virtustream, discussed the evolution of the company from inception to its recent acquisition by EMC – including personal insights, lessons learned (and some WTF moments) along the way. Learn how Virtustream’s unique approach of combining the economics and elasticity of the consumer cloud model with proper performance, application automation and security into a platform became a breakout success with enterprise customers and a natural fit for the EMC Federation.
The Internet of Things is not only adding billions of sensors and billions of terabytes to the Internet. It is also forcing a fundamental change in the way we envision Information Technology. For the first time, more data is being created by devices at the edge of the Internet rather than from centralized systems. What does this mean for today's IT professional? In this Power Panel at @ThingsExpo, moderated by Conference Chair Roger Strukhoff, panelists addressed this very serious issue of profound change in the industry.
Discussions about cloud computing are evolving into discussions about enterprise IT in general. As enterprises increasingly migrate toward their own unique clouds, new issues such as the use of containers and microservices emerge to keep things interesting. In this Power Panel at 16th Cloud Expo, moderated by Conference Chair Roger Strukhoff, panelists addressed the state of cloud computing today, and what enterprise IT professionals need to know about how the latest topics and trends affect their organization.
It is one thing to build single industrial IoT applications, but what will it take to build the Smart Cities and truly society-changing applications of the future? The technology won’t be the problem, it will be the number of parties that need to work together and be aligned in their motivation to succeed. In his session at @ThingsExpo, Jason Mondanaro, Director, Product Management at Metanga, discussed how you can plan to cooperate, partner, and form lasting all-star teams to change the world and it starts with business models and monetization strategies.
Converging digital disruptions is creating a major sea change - Cisco calls this the Internet of Everything (IoE). IoE is the network connection of People, Process, Data and Things, fueled by Cloud, Mobile, Social, Analytics and Security, and it represents a $19Trillion value-at-stake over the next 10 years. In her keynote at @ThingsExpo, Manjula Talreja, VP of Cisco Consulting Services, discussed IoE and the enormous opportunities it provides to public and private firms alike. She will share what businesses must do to thrive in the IoE economy, citing examples from several industry sectors.
There will be 150 billion connected devices by 2020. New digital businesses have already disrupted value chains across every industry. APIs are at the center of the digital business. You need to understand what assets you have that can be exposed digitally, what their digital value chain is, and how to create an effective business model around that value chain to compete in this economy. No enterprise can be complacent and not engage in the digital economy. Learn how to be the disruptor and not the disruptee.
Akana has released Envision, an enhanced API analytics platform that helps enterprises mine critical insights across their digital eco-systems, understand their customers and partners and offer value-added personalized services. “In today’s digital economy, data-driven insights are proving to be a key differentiator for businesses. Understanding the data that is being tunneled through their APIs and how it can be used to optimize their business and operations is of paramount importance,” said Alistair Farquharson, CTO of Akana.
Business as usual for IT is evolving into a "Make or Buy" decision on a service-by-service conversation with input from the LOBs. How does your organization move forward with cloud? In his general session at 16th Cloud Expo, Paul Maravei, Regional Sales Manager, Hybrid Cloud and Managed Services at Cisco, discusses how Cisco and its partners offer a market-leading portfolio and ecosystem of cloud infrastructure and application services that allow you to uniquely and securely combine cloud business applications and services across multiple cloud delivery models.
The enterprise market will drive IoT device adoption over the next five years. In his session at @ThingsExpo, John Greenough, an analyst at BI Intelligence, division of Business Insider, analyzed how companies will adopt IoT products and the associated cost of adopting those products. John Greenough is the lead analyst covering the Internet of Things for BI Intelligence- Business Insider’s paid research service. Numerous IoT companies have cited his analysis of the IoT. Prior to joining BI Intelligence, he worked analyzing bank technology for Corporate Insight and The Clearing House Payment...
"Optimal Design is a technology integration and product development firm that specializes in connecting devices to the cloud," stated Joe Wascow, Co-Founder & CMO of Optimal Design, in this SYS-CON.tv interview at @ThingsExpo, held June 9-11, 2015, at the Javits Center in New York City.
SYS-CON Events announced today that CommVault has been named “Bronze Sponsor” of SYS-CON's 17th International Cloud Expo®, which will take place on November 3–5, 2015, at the Santa Clara Convention Center in Santa Clara, CA. A singular vision – a belief in a better way to address current and future data management needs – guides CommVault in the development of Singular Information Management® solutions for high-performance data protection, universal availability and simplified management of data on complex storage networks. CommVault's exclusive single-platform architecture gives companies unp...
Electric Cloud and Arynga have announced a product integration partnership that will bring Continuous Delivery solutions to the automotive Internet-of-Things (IoT) market. The joint solution will help automotive manufacturers, OEMs and system integrators adopt DevOps automation and Continuous Delivery practices that reduce software build and release cycle times within the complex and specific parameters of embedded and IoT software systems.
"ciqada is a combined platform of hardware modules and server products that lets people take their existing devices or new devices and lets them be accessible over the Internet for their users," noted Geoff Engelstein of ciqada, a division of Mars International, in this SYS-CON.tv interview at @ThingsExpo, held June 9-11, 2015, at the Javits Center in New York City.
Internet of Things is moving from being a hype to a reality. Experts estimate that internet connected cars will grow to 152 million, while over 100 million internet connected wireless light bulbs and lamps will be operational by 2020. These and many other intriguing statistics highlight the importance of Internet powered devices and how market penetration is going to multiply many times over in the next few years.