Welcome!

Java IoT Authors: Liz McMillan, APM Blog, Elizabeth White, Stackify Blog, Yeshim Deniz

Related Topics: Java IoT

Java IoT: Article

101 on jQuery Selector Performance

jQuery selectors and their performance Impact

Java Developer Magazine on Ulitzer

Last week I analyzed a web page that spent 4.8 seconds in the onLoad event handler of a custom script file. It turned out that 2.8 seconds were consumed by applying a dynamic menu library (will blog about this one separately). The remaining 2 seconds were spent in jQuery selectors. The analysis showed that most of the selectors didn’t return any object and those that returned objects can be improved by using different selectors.

About jQuery Selectors
There are some great blog articles about jQuery Selectors and their Performance Impact. As you can see you can select elements by ID, TagName or ClassName. Depending on the select jQuery can use the native browser methods to query elements by id or tag or needs to manually iterate through the DOM in case of class names (as there is not getElementsByClassName in IE).

Analyzing the 2 seconds in my page time
The onLoad handler uses jQuery to set hide, show, change style sheets, … for certain elements on the page. Here is a code snippet:

Sample jQuery Script exected in onLoad

Sample jQuery Script exected in onLoad
The onLoad event handler was full of these calls. Using the free dynaTrace AJAX Edition you can see the individual $ calls that resolves the selector and the following method call in case the selector resolved at least one object. The following PurePath of the onLoad event handler not only shows me how much time was spent in those selector calls – but also how many of these actually didn’t find a single object (the lack of the following method call indicates that no object was found):

Unnecessary jQuery Selector Calls causing massive overhead

Unnecessary jQuery Selector Calls causing massive overhead

All calls marked in red are calls that didn’t return an element because there was no DOM element based on the selection criteria. The JS column shows the execution time of each individual method call – ranging from 1ms to > 100ms per call. The size column tells us how many JavaScript/DOM calls were made by an individual call. Here we can also see why certain $ calls took so much longer as they made many calls to fulfil the request. The Invocation column tells me how often a method was invoked by its parent. We can see here that some objects were actually resolved multiple times, e.g.: “.pop-cart”. It would have been better to only resolve it once and cache the object.

The first lesson learned from this is that most of these calls were not necessary and just caused massive overhead. If you happen to know which elements are on a page you should only resolve those objects and don’t try to resolve others. I know – having global java script files that handle different pages with different content cause a situation like this – but – do you really want to live with this overhead?

Analyzing difference in jQuery Selectors
The first problem on the analyzed page was that too many unnecessary $ calls were made. The other question that came up was why certain $ methods respond very fast (some milliseconds) where others take rather long (up to 100ms). The theoretical answer can be found in the jQuery Best Practice Blog. Coming back to my page shows me the following:

Selector by ID is the fastest using getElementById

Following image shows a selector using an ID. It uses getElementById and therefore returns very fast.

jQuery Selector by ID

jQuery Selector by ID

Selector by TagName using getElementsByTag
The following example selects elements by TagName and ClassName. jQuery first uses the getElementsByTagName which is a native implementation to retrieve all elements for the specified tag. jQuery then iterates through these items to filter for the ClassName.

jQuery Selector by Tag and ClassName

jQuery Selector by Tag and ClassName

Selector by ClassName needs to iterate through ALL DOM elements
If you use a selector by ClassName only – jQuery needs to iterate through EVERY element in the DOM as there is no native implementation for getElementsByClassName in Internet Explorer (its a different story for FireFox). Following image shows the overhead of a selector on a page with 3460 DOM Elements:

jQuery Selector by Class Name

jQuery Selector by Class Name

Conclusion
Depending on the size of your web site (number of DOM elements) you should consider the overhead of individual selector methods. Instead of selecting by classname you may want to think about using TagName and ClassName or by using unique IDs in case you only have a handful of objects on your page. Also – make sure you cache already resolved objects to avoid the overhead for subsequent resolving calls. And – last but not least – avoid calls that are not necessary. As seen in the page that I analyzed – more than 1.5 seconds of the 2 seconds can be saved by not making those calls.

Related reading:

  1. 101 on Prototype CSS Selectors Performance implications of certain CSS Selectors are not specific to...
  2. Performance Analysis of dynamic JavaScript Menus In my previous post I talked about the impact of...
  3. How to Speed Up sites like vancouver2010.com by more than 50% in 5 minutes Many Web Sites that use JavaScript frameworks to make the...
  4. How to test jQuery enabled Apps using JSON with Visual Studio Visual Studio Team System offers a nice Web- and Load-Testing...
  5. Ensuring Web Site Performance – Why, What and How to Measure Automated and Accurately It is a fact that end user response time is...

More Stories By Andreas Grabner

Andreas Grabner has been helping companies improve their application performance for 15+ years. He is a regular contributor within Web Performance and DevOps communities and a prolific speaker at user groups and conferences around the world. Reach him at @grabnerandi

@ThingsExpo Stories
Gemini is Yahoo’s native and search advertising platform. To ensure the quality of a complex distributed system that spans multiple products and components and across various desktop websites and mobile app and web experiences – both Yahoo owned and operated and third-party syndication (supply), with complex interaction with more than a billion users and numerous advertisers globally (demand) – it becomes imperative to automate a set of end-to-end tests 24x7 to detect bugs and regression. In th...
"Space Monkey by Vivent Smart Home is a product that is a distributed cloud-based edge storage network. Vivent Smart Home, our parent company, is a smart home provider that places a lot of hard drives across homes in North America," explained JT Olds, Director of Engineering, and Brandon Crowfeather, Product Manager, at Vivint Smart Home, in this SYS-CON.tv interview at @ThingsExpo, held Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA.
"IBM is really all in on blockchain. We take a look at sort of the history of blockchain ledger technologies. It started out with bitcoin, Ethereum, and IBM evaluated these particular blockchain technologies and found they were anonymous and permissionless and that many companies were looking for permissioned blockchain," stated René Bostic, Technical VP of the IBM Cloud Unit in North America, in this SYS-CON.tv interview at 21st Cloud Expo, held Oct 31 – Nov 2, 2017, at the Santa Clara Conventi...
"Cloud Academy is an enterprise training platform for the cloud, specifically public clouds. We offer guided learning experiences on AWS, Azure, Google Cloud and all the surrounding methodologies and technologies that you need to know and your teams need to know in order to leverage the full benefits of the cloud," explained Alex Brower, VP of Marketing at Cloud Academy, in this SYS-CON.tv interview at 21st Cloud Expo, held Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clar...
It is of utmost importance for the future success of WebRTC to ensure that interoperability is operational between web browsers and any WebRTC-compliant client. To be guaranteed as operational and effective, interoperability must be tested extensively by establishing WebRTC data and media connections between different web browsers running on different devices and operating systems. In his session at WebRTC Summit at @ThingsExpo, Dr. Alex Gouaillard, CEO and Founder of CoSMo Software, presented ...
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, whic...
Coca-Cola’s Google powered digital signage system lays the groundwork for a more valuable connection between Coke and its customers. Digital signs pair software with high-resolution displays so that a message can be changed instantly based on what the operator wants to communicate or sell. In their Day 3 Keynote at 21st Cloud Expo, Greg Chambers, Global Group Director, Digital Innovation, Coca-Cola, and Vidya Nagarajan, a Senior Product Manager at Google, discussed how from store operations and ...
In his session at 21st Cloud Expo, Carl J. Levine, Senior Technical Evangelist for NS1, will objectively discuss how DNS is used to solve Digital Transformation challenges in large SaaS applications, CDNs, AdTech platforms, and other demanding use cases. Carl J. Levine is the Senior Technical Evangelist for NS1. A veteran of the Internet Infrastructure space, he has over a decade of experience with startups, networking protocols and Internet infrastructure, combined with the unique ability to it...
"MobiDev is a software development company and we do complex, custom software development for everybody from entrepreneurs to large enterprises," explained Alan Winters, U.S. Head of Business Development at MobiDev, in this SYS-CON.tv interview at 21st Cloud Expo, held Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA.
SYS-CON Events announced today that CrowdReviews.com has been named “Media Sponsor” of SYS-CON's 22nd International Cloud Expo, which will take place on June 5–7, 2018, 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 buye...
"There's plenty of bandwidth out there but it's never in the right place. So what Cedexis does is uses data to work out the best pathways to get data from the origin to the person who wants to get it," explained Simon Jones, Evangelist and Head of Marketing at Cedexis, in this SYS-CON.tv interview at 21st Cloud Expo, held Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA.
WebRTC is great technology to build your own communication tools. It will be even more exciting experience it with advanced devices, such as a 360 Camera, 360 microphone, and a depth sensor camera. In his session at @ThingsExpo, Masashi Ganeko, a manager at INFOCOM Corporation, introduced two experimental projects from his team and what they learned from them. "Shotoku Tamago" uses the robot audition software HARK to track speakers in 360 video of a remote party. "Virtual Teleport" uses a multip...
SYS-CON Events announced today that Telecom Reseller has been named “Media Sponsor” of SYS-CON's 22nd International Cloud Expo, which will take place on June 5-7, 2018, at the Javits Center in New York, 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.
SYS-CON Events announced today that Evatronix will exhibit at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Evatronix SA offers comprehensive solutions in the design and implementation of electronic systems, in CAD / CAM deployment, and also is a designer and manufacturer of advanced 3D scanners for professional applications.
Leading companies, from the Global Fortune 500 to the smallest companies, are adopting hybrid cloud as the path to business advantage. Hybrid cloud depends on cloud services and on-premises infrastructure working in unison. Successful implementations require new levels of data mobility, enabled by an automated and seamless flow across on-premises and cloud resources. In his general session at 21st Cloud Expo, Greg Tevis, an IBM Storage Software Technical Strategist and Customer Solution Architec...
To get the most out of their data, successful companies are not focusing on queries and data lakes, they are actively integrating analytics into their operations with a data-first application development approach. Real-time adjustments to improve revenues, reduce costs, or mitigate risk rely on applications that minimize latency on a variety of data sources. In his session at @BigDataExpo, Jack Norris, Senior Vice President, Data and Applications at MapR Technologies, reviewed best practices to ...
An increasing number of companies are creating products that combine data with analytical capabilities. Running interactive queries on Big Data requires complex architectures to store and query data effectively, typically involving data streams, an choosing efficient file format/database and multiple independent systems that are tied together through custom-engineered pipelines. In his session at @BigDataExpo at @ThingsExpo, Tomer Levi, a senior software engineer at Intel’s Advanced Analytics gr...
When talking IoT we often focus on the devices, the sensors, the hardware itself. The new smart appliances, the new smart or self-driving cars (which are amalgamations of many ‘things’). When we are looking at the world of IoT, we should take a step back, look at the big picture. What value are these devices providing? IoT is not about the devices, it’s about the data consumed and generated. The devices are tools, mechanisms, conduits. In his session at Internet of Things at Cloud Expo | DXWor...
Everything run by electricity will eventually be connected to the Internet. Get ahead of the Internet of Things revolution. In his session at @ThingsExpo, Akvelon expert and IoT industry leader Sergey Grebnov provided an educational dive into the world of managing your home, workplace and all the devices they contain with the power of machine-based AI and intelligent Bot services for a completely streamlined experience.
SYS-CON Events announced today that Synametrics Technologies will exhibit at SYS-CON's 22nd International Cloud Expo®, which will take place on June 5-7, 2018, at the Javits Center in New York, NY. Synametrics Technologies is a privately held company based in Plainsboro, New Jersey that has been providing solutions for the developer community since 1997. Based on the success of its initial product offerings such as WinSQL, Xeams, SynaMan and Syncrify, Synametrics continues to create and hone inn...