Welcome!

Java IoT Authors: Sanjeev Khurana, Elizabeth White, Carmen Gonzalez, Patrick Hubbard, Liz McMillan

Related Topics: Java IoT, Microservices Expo, IBM Cloud, Weblogic, Machine Learning , 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 CA Technologies has been named “Platinum Sponsor” of SYS-CON's 20th International Cloud Expo®, which will take place on June 6-8, 2017, at the Javits Center in New York City, NY, and the 21st International Cloud Expo®, which will take place October 31-November 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. CA Technologies helps customers succeed in a future where every business – from apparel to energy – is being rewritten by software. From ...
SYS-CON Events announced today that Cloudistics, an on-premises cloud computing company, has been named “Bronze Sponsor” of SYS-CON's 20th International Cloud Expo®, which will take place on June 6-8, 2017, at the Javits Center in New York City, NY. Cloudistics delivers a complete public cloud experience with composable on-premises infrastructures to medium and large enterprises. Its software-defined technology natively converges network, storage, compute, virtualization, and management into a ...
Keeping pace with advancements in software delivery processes and tooling is taxing even for the most proficient organizations. Point tools, platforms, open source and the increasing adoption of private and public cloud services requires strong engineering rigor - all in the face of developer demands to use the tools of choice. As Agile has settled in as a mainstream practice, now DevOps has emerged as the next wave to improve software delivery speed and output. To make DevOps work, organization...
My team embarked on building a data lake for our sales and marketing data to better understand customer journeys. This required building a hybrid data pipeline to connect our cloud CRM with the new Hadoop Data Lake. One challenge is that IT was not in a position to provide support until we proved value and marketing did not have the experience, so we embarked on the journey ourselves within the product marketing team for our line of business within Progress. In his session at @BigDataExpo, Sum...
SYS-CON Events announced today that Ocean9will exhibit at SYS-CON's 20th International Cloud Expo®, which will take place on June 6-8, 2017, at the Javits Center in New York City, NY. Ocean9 provides cloud services for Backup, Disaster Recovery (DRaaS) and instant Innovation, and redefines enterprise infrastructure with its cloud native subscription offerings for mission critical SAP workloads.
DevOps is often described as a combination of technology and culture. Without both, DevOps isn't complete. However, applying the culture to outdated technology is a recipe for disaster; as response times grow and connections between teams are delayed by technology, the culture will die. A Nutanix Enterprise Cloud has many benefits that provide the needed base for a true DevOps paradigm.
With major technology companies and startups seriously embracing Cloud strategies, now is the perfect time to attend @CloudExpo | @ThingsExpo, June 6-8, 2017, at the Javits Center in New York City, NY and October 31 - November 2, 2017, Santa Clara Convention Center, CA. Learn what is going on, contribute to the discussions, and ensure that your enterprise is on the right path to Digital Transformation.
SYS-CON Events announced today that T-Mobile will exhibit at SYS-CON's 20th International Cloud Expo®, which will take place on June 6-8, 2017, at the Javits Center in New York City, NY. As America's Un-carrier, T-Mobile US, Inc., is redefining the way consumers and businesses buy wireless services through leading product and service innovation. The Company's advanced nationwide 4G LTE network delivers outstanding wireless experiences to 67.4 million customers who are unwilling to compromise on ...
SYS-CON Events announced today that SoftLayer, an IBM Company, has been named “Gold Sponsor” of SYS-CON's 18th Cloud Expo, which will take place on June 7-9, 2016, at the Javits Center in New York, New York. SoftLayer, an IBM Company, provides cloud infrastructure as a service from a growing number of data centers and network points of presence around the world. SoftLayer’s customers range from Web startups to global enterprises.
SYS-CON Events announced today that CrowdReviews.com has been named “Media Sponsor” of SYS-CON's 20th International Cloud Expo, which will take place on June 6–8, 2017, at the Javits Center in New York City, NY. CrowdReviews.com is a transparent online platform for determining which products and services are the best based on the opinion of the crowd. The crowd consists of Internet users that have experienced products and services first-hand and have an interest in letting other potential buyers...
The taxi industry never saw Uber coming. Startups are a threat to incumbents like never before, and a major enabler for startups is that they are instantly “cloud ready.” If innovation moves at the pace of IT, then your company is in trouble. Why? Because your data center will not keep up with frenetic pace AWS, Microsoft and Google are rolling out new capabilities In his session at 20th Cloud Expo, Don Browning, VP of Cloud Architecture at Turner, will posit that disruption is inevitable for c...
SYS-CON Events announced today that Infranics will exhibit at SYS-CON's 20th International Cloud Expo®, which will take place on June 6-8, 2017, at the Javits Center in New York City, NY. Since 2000, Infranics has developed SysMaster Suite, which is required for the stable and efficient management of ICT infrastructure. The ICT management solution developed and provided by Infranics continues to add intelligence to the ICT infrastructure through the IMC (Infra Management Cycle) based on mathemat...
SYS-CON Events announced today that SD Times | BZ Media has been named “Media Sponsor” of SYS-CON's 20th International Cloud Expo, which will take place on June 6–8, 2017, at the Javits Center in New York City, NY. BZ Media LLC is a high-tech media company that produces technical conferences and expositions, and publishes a magazine, newsletters and websites in the software development, SharePoint, mobile development and commercial UAV markets.
Now that the world has connected “things,” we need to build these devices as truly intelligent in order to create instantaneous and precise results. This means you have to do as much of the processing at the point of entry as you can: at the edge. The killer use cases for IoT are becoming manifest through AI engines on edge devices. An autonomous car has this dual edge/cloud analytics model, producing precise, real-time results. In his session at @ThingsExpo, John Crupi, Vice President and Eng...
SYS-CON Events announced today that Telecom Reseller has been named “Media Sponsor” of SYS-CON's 20th International Cloud Expo, which will take place on June 6–8, 2017, at the Javits Center in New York City, NY. Telecom Reseller reports on Unified Communications, UCaaS, BPaaS for enterprise and SMBs. They report extensively on both customer premises based solutions such as IP-PBX as well as cloud based and hosted platforms.
In his General Session at 16th Cloud Expo, David Shacochis, host of The Hybrid IT Files podcast and Vice President at CenturyLink, investigated three key trends of the “gigabit economy" though the story of a Fortune 500 communications company in transformation. Narrating how multi-modal hybrid IT, service automation, and agile delivery all intersect, he will cover the role of storytelling and empathy in achieving strategic alignment between the enterprise and its information technology.
The buzz continues for cloud, data analytics and the Internet of Things (IoT) and their collective impact across all industries. But a new conversation is emerging - how do companies use industry disruption and technology enablers to lead in markets undergoing change, uncertainty and ambiguity? Organizations of all sizes need to evolve and transform, often under massive pressure, as industry lines blur and merge and traditional business models are assaulted and turned upside down. In this new da...
Web Real-Time Communication APIs have quickly revolutionized what browsers are capable of. In addition to video and audio streams, we can now bi-directionally send arbitrary data over WebRTC's PeerConnection Data Channels. With the advent of Progressive Web Apps and new hardware APIs such as WebBluetooh and WebUSB, we can finally enable users to stitch together the Internet of Things directly from their browsers while communicating privately and securely in a decentralized way.
SYS-CON Events announced today that MobiDev, a client-oriented software development company, will exhibit at SYS-CON's 20th International Cloud Expo®, which will take place June 6-8, 2017, at the Javits Center in New York City, NY, and the 21st International Cloud Expo®, which will take place October 31-November 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. MobiDev is a software company that develops and delivers turn-key mobile apps, websites, web services, and complex softw...
SYS-CON Events announced today that HTBase will exhibit at SYS-CON's 20th International Cloud Expo®, which will take place on June 6-8, 2017, at the Javits Center in New York City, NY. HTBase (Gartner 2016 Cool Vendor) delivers a Composable IT infrastructure solution architected for agility and increased efficiency. It turns compute, storage, and fabric into fluid pools of resources that are easily composed and re-composed to meet each application’s needs. With HTBase, companies can quickly prov...