Welcome!

Apache Authors: William Schmarzo, Christopher Harrold, Elizabeth White, Talend Inc., Adrian Bridgwater

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
Connected devices and the industrial internet are growing exponentially every year with Cisco expecting 50 billion devices to be in operation by 2020. In this period of growth, location-based insights are becoming invaluable to many businesses as they adopt new connected technologies. Knowing when and where these devices connect from is critical for a number of scenarios in supply chain management, disaster management, emergency response, M2M, location marketing and more. In his session at @Th...
Extracting business value from Internet of Things (IoT) data doesn’t happen overnight. There are several requirements that must be satisfied, including IoT device enablement, data analysis, real-time detection of complex events and automated orchestration of actions. Unfortunately, too many companies fall short in achieving their business goals by implementing incomplete solutions or not focusing on tangible use cases. In his general session at @ThingsExpo, Dave McCarthy, Director of Products...
There are several IoTs: the Industrial Internet, Consumer Wearables, Wearables and Healthcare, Supply Chains, and the movement toward Smart Grids, Cities, Regions, and Nations. There are competing communications standards every step of the way, a bewildering array of sensors and devices, and an entire world of competing data analytics platforms. To some this appears to be chaos. In this power panel at @ThingsExpo, moderated by Conference Chair Roger Strukhoff, Bradley Holt, Developer Advocate a...
The Internet of Things will challenge the status quo of how IT and development organizations operate. Or will it? Certainly the fog layer of IoT requires special insights about data ontology, security and transactional integrity. But the developmental challenges are the same: People, Process and Platform and how we integrate our thinking to solve complicated problems. In his session at 19th Cloud Expo, Craig Sproule, CEO of Metavine, will demonstrate how to move beyond today's coding paradigm ...
"There's a growing demand from users for things to be faster. When you think about all the transactions or interactions users will have with your product and everything that is between those transactions and interactions - what drives us at Catchpoint Systems is the idea to measure that and to analyze it," explained Leo Vasiliou, Director of Web Performance Engineering at Catchpoint Systems, in this SYS-CON.tv interview at 18th Cloud Expo, held June 7-9, 2016, at the Javits Center in New York Ci...
Apixio Inc. has raised $19.3 million in Series D venture capital funding led by SSM Partners with participation from First Analysis, Bain Capital Ventures and Apixio’s largest angel investor. Apixio will dedicate the proceeds toward advancing and scaling products powered by its cognitive computing platform, further enabling insights for optimal patient care. The Series D funding comes as Apixio experiences strong momentum and increasing demand for its HCC Profiler solution, which mines unstruc...
SYS-CON Events has announced today that Roger Strukhoff has been named conference chair of Cloud Expo and @ThingsExpo 2016 Silicon Valley. The 19th Cloud Expo and 6th @ThingsExpo will take place on November 1-3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. "The Internet of Things brings trillions of dollars of opportunity to developers and enterprise IT, no matter how you measure it," stated Roger Strukhoff. "More importantly, it leverages the power of devices and the Interne...
In addition to all the benefits, IoT is also bringing new kind of customer experience challenges - cars that unlock themselves, thermostats turning houses into saunas and baby video monitors broadcasting over the internet. This list can only increase because while IoT services should be intuitive and simple to use, the delivery ecosystem is a myriad of potential problems as IoT explodes complexity. So finding a performance issue is like finding the proverbial needle in the haystack.
Machine Learning helps make complex systems more efficient. By applying advanced Machine Learning techniques such as Cognitive Fingerprinting, wind project operators can utilize these tools to learn from collected data, detect regular patterns, and optimize their own operations. In his session at 18th Cloud Expo, Stuart Gillen, Director of Business Development at SparkCognition, discussed how research has demonstrated the value of Machine Learning in delivering next generation analytics to imp...
Whether your IoT service is connecting cars, homes, appliances, wearable, cameras or other devices, one question hangs in the balance – how do you actually make money from this service? The ability to turn your IoT service into profit requires the ability to create a monetization strategy that is flexible, scalable and working for you in real-time. It must be a transparent, smoothly implemented strategy that all stakeholders – from customers to the board – will be able to understand and comprehe...
The cloud market growth today is largely in public clouds. While there is a lot of spend in IT departments in virtualization, these aren’t yet translating into a true “cloud” experience within the enterprise. What is stopping the growth of the “private cloud” market? In his general session at 18th Cloud Expo, Nara Rajagopalan, CEO of Accelerite, explored the challenges in deploying, managing, and getting adoption for a private cloud within an enterprise. What are the key differences between wh...
Ask someone to architect an Internet of Things (IoT) solution and you are guaranteed to see a reference to the cloud. This would lead you to believe that IoT requires the cloud to exist. However, there are many IoT use cases where the cloud is not feasible or desirable. In his session at @ThingsExpo, Dave McCarthy, Director of Products at Bsquare Corporation, will discuss the strategies that exist to extend intelligence directly to IoT devices and sensors, freeing them from the constraints of ...
The IoT is changing the way enterprises conduct business. In his session at @ThingsExpo, Eric Hoffman, Vice President at EastBanc Technologies, discussed how businesses can gain an edge over competitors by empowering consumers to take control through IoT. He cited examples such as a Washington, D.C.-based sports club that leveraged IoT and the cloud to develop a comprehensive booking system. He also highlighted how IoT can revitalize and restore outdated business models, making them profitable ...
IoT offers a value of almost $4 trillion to the manufacturing industry through platforms that can improve margins, optimize operations & drive high performance work teams. By using IoT technologies as a foundation, manufacturing customers are integrating worker safety with manufacturing systems, driving deep collaboration and utilizing analytics to exponentially increased per-unit margins. However, as Benoit Lheureux, the VP for Research at Gartner points out, “IoT project implementers often ...
When people aren’t talking about VMs and containers, they’re talking about serverless architecture. Serverless is about no maintenance. It means you are not worried about low-level infrastructural and operational details. An event-driven serverless platform is a great use case for IoT. In his session at @ThingsExpo, Animesh Singh, an STSM and Lead for IBM Cloud Platform and Infrastructure, will detail how to build a distributed serverless, polyglot, microservices framework using open source tec...
The idea of comparing data in motion (at the sensor level) to data at rest (in a Big Data server warehouse) with predictive analytics in the cloud is very appealing to the industrial IoT sector. The problem Big Data vendors have, however, is access to that data in motion at the sensor location. In his session at @ThingsExpo, Scott Allen, CMO of FreeWave, discussed how as IoT is increasingly adopted by industrial markets, there is going to be an increased demand for sensor data from the outermos...
CenturyLink has announced that application server solutions from GENBAND are now available as part of CenturyLink’s Networx contracts. The General Services Administration (GSA)’s Networx program includes the largest telecommunications contract vehicles ever awarded by the federal government. CenturyLink recently secured an extension through spring 2020 of its offerings available to federal government agencies via GSA’s Networx Universal and Enterprise contracts. GENBAND’s EXPERiUS™ Application...
A strange thing is happening along the way to the Internet of Things, namely far too many devices to work with and manage. It has become clear that we'll need much higher efficiency user experiences that can allow us to more easily and scalably work with the thousands of devices that will soon be in each of our lives. Enter the conversational interface revolution, combining bots we can literally talk with, gesture to, and even direct with our thoughts, with embedded artificial intelligence, wh...
"delaPlex is a software development company. We do team-based outsourcing development," explained Mark Rivers, COO and Co-founder of delaPlex Software, in this SYS-CON.tv interview at 18th Cloud Expo, held June 7-9, 2016, at the Javits Center in New York City, NY.
"We work in the area of Big Data analytics and Big Data analytics is a very crowded space - you have Hadoop, ETL, warehousing, visualization and there's a lot of effort trying to get these tools to talk to each other," explained Mukund Deshpande, head of the Analytics practice at Accelerite, in this SYS-CON.tv interview at 18th Cloud Expo, held June 7-9, 2016, at the Javits Center in New York City, NY.