Welcome!

IoT User Interface Authors: Elizabeth White, Yakov Fain, John Basso, Derek Weeks, Asim Saddal

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.


@CloudExpo Stories
SYS-CON Events announced today that 910Telecom will exhibit at the 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. Housed in the classic Denver Gas & Electric Building, 910 15th St., 910Telecom is a carrier-neutral telecom hotel located in the heart of Denver. Adjacent to CenturyLink, AT&T, and Denver Main, 910Telecom offers connectivity to all major carriers, Internet service providers, Internet backbones and ...
Traditional on-premises data centers have long been the domain of modern data platforms like Apache Hadoop, meaning companies who build their business on public cloud were challenged to run Big Data processing and analytics at scale. But recent advancements in Hadoop performance, security, and most importantly cloud-native integrations, are giving organizations the ability to truly gain value from all their data. In his session at 19th Cloud Expo, David Tishgart, Director of Product Marketing ...
Almost two-thirds of companies either have or soon will have IoT as the backbone of their business in 2016. However, IoT is far more complex than most firms expected. How can you not get trapped in the pitfalls? In his session at @ThingsExpo, Tony Shan, a renowned visionary and thought leader, will introduce a holistic method of IoTification, which is the process of IoTifying the existing technology and business models to adopt and leverage IoT. He will drill down to the components in this fra...
StarNet Communications Corp has announced the addition of three Secure Remote Desktop modules to its flagship X-Win32 PC X server. The new modules enable X-Win32 to safely tunnel the remote desktops from Linux and Unix servers to the user’s PC over encrypted SSH. Traditionally, users of PC X servers deploy the XDMCP protocol to display remote desktop environments such as the Gnome and KDE desktops on Linux servers and the CDE environment on Solaris Unix machines. XDMCP is used primarily on comp...
DevOps at Cloud Expo – being held November 1-3, 2016, at the Santa Clara Convention Center in Santa Clara, CA – announces that its Call for Papers is open. Born out of proven success in agile development, cloud computing, and process automation, DevOps is a macro trend you cannot afford to miss. From showcase success stories from early adopters and web-scale businesses, DevOps is expanding to organizations of all sizes, including the world's largest enterprises – and delivering real results. Am...
Internet of @ThingsExpo, taking place November 1-3, 2016, at the Santa Clara Convention Center in Santa Clara, CA, is co-located with 19th Cloud Expo and will feature technical sessions from a rock star conference faculty and the leading industry players in the world. The Internet of Things (IoT) is the most profound change in personal and enterprise IT since the creation of the Worldwide Web more than 20 years ago. All major researchers estimate there will be tens of billions devices - comp...
As the world moves toward more DevOps and Microservices, application deployment to the cloud ought to become a lot simpler. The Microservices architecture, which is the basis of many new age distributed systems such as OpenStack, NetFlix and so on, is at the heart of Cloud Foundry - a complete developer-oriented Platform as a Service (PaaS) that is IaaS agnostic and supports vCloud, OpenStack and AWS. Serverless computing is revolutionizing computing. In his session at 19th Cloud Expo, Raghav...
DevOps at Cloud Expo, taking place Nov 1-3, 2016, at the Santa Clara Convention Center in Santa Clara, CA, is co-located with 19th Cloud Expo and will feature technical sessions from a rock star conference faculty and the leading industry players in the world. The widespread success of cloud computing is driving the DevOps revolution in enterprise IT. Now as never before, development teams must communicate and collaborate in a dynamic, 24/7/365 environment. There is no time to wait for long dev...
Data is the fuel that drives the machine learning algorithmic engines and ultimately provides the business value. In his session at Cloud Expo, Ed Featherston, a director and senior enterprise architect at Collaborative Consulting, will discuss the key considerations around quality, volume, timeliness, and pedigree that must be dealt with in order to properly fuel that engine.
There is growing need for data-driven applications and the need for digital platforms to build these apps. In his session at 19th Cloud Expo, Muddu Sudhakar, VP and GM of Security & IoT at Splunk, will cover different PaaS solutions and Big Data platforms that are available to build applications. In addition, AI and machine learning are creating new requirements that developers need in the building of next-gen apps. The next-generation digital platforms have some of the past platform needs a...
Fact: storage performance problems have only gotten more complicated, as applications not only have become largely virtualized, but also have moved to cloud-based infrastructures. Storage performance in virtualized environments isn’t just about IOPS anymore. Instead, you need to guarantee performance for individual VMs, helping applications maintain performance as the number of VMs continues to go up in real time. In his session at Cloud Expo, Dhiraj Sehgal, Product and Marketing at Tintri, wil...
19th Cloud Expo, taking place November 1-3, 2016, at the Santa Clara Convention Center in Santa Clara, CA, will feature technical sessions from a rock star conference faculty and the leading industry players in the world. Cloud computing is now being embraced by a majority of enterprises of all sizes. Yesterday's debate about public vs. private has transformed into the reality of hybrid cloud: a recent survey shows that 74% of enterprises have a hybrid cloud strategy. Meanwhile, 94% of enterpri...
Enterprises have forever faced challenges surrounding the sharing of their intellectual property. Emerging cloud adoption has made it more compelling for enterprises to digitize their content, making them available over a wide variety of devices across the Internet. In his session at 19th Cloud Expo, Santosh Ahuja, Director of Architecture at Impiger Technologies, will introduce various mechanisms provided by cloud service providers today to manage and share digital content in a secure manner....
SYS-CON Events announced today that Hitrons Solutions will exhibit at the 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. Hitrons Solutions Inc. is distributor in the North American market for unique products and services of small and medium-size businesses, including cloud services and solutions, SEO marketing platforms, and mobile applications.
SYS-CON Events announced today that eCube Systems, a leading provider of middleware modernization, integration, and management solutions, will exhibit at @DevOpsSummit at 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. eCube Systems offers a family of middleware evolution products and services that maximize return on technology investment by leveraging existing technical equity to meet evolving business needs. ...
SYS-CON Events announced today Telecom Reseller has been named “Media Sponsor” of SYS-CON's 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. 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.
Pulzze Systems was happy to participate in such a premier event and thankful to be receiving the winning investment and global network support from G-Startup Worldwide. It is an exciting time for Pulzze to showcase the effectiveness of innovative technologies and enable them to make the world smarter and better. The reputable contest is held to identify promising startups around the globe that are assured to change the world through their innovative products and disruptive technologies. There w...
SYS-CON Events announced today that Isomorphic Software will exhibit at DevOps Summit at 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. Isomorphic Software provides the SmartClient HTML5/AJAX platform, the most advanced technology for building rich, cutting-edge enterprise web applications for desktop and mobile. SmartClient combines the productivity and performance of traditional desktop software with the simp...
With so much going on in this space you could be forgiven for thinking you were always working with yesterday’s technologies. So much change, so quickly. What do you do if you have to build a solution from the ground up that is expected to live in the field for at least 5-10 years? This is the challenge we faced when we looked to refresh our existing 10-year-old custom hardware stack to measure the fullness of trash cans and compactors.
Extreme Computing is the ability to leverage highly performant infrastructure and software to accelerate Big Data, machine learning, HPC, and Enterprise applications. High IOPS Storage, low-latency networks, in-memory databases, GPUs and other parallel accelerators are being used to achieve faster results and help businesses make better decisions. In his session at 18th Cloud Expo, Michael O'Neill, Strategic Business Development at NVIDIA, focused on some of the unique ways extreme computing is...