Challenges with Monitoring Knockout.js Web Applications

Web applications like knockout.js help you to reach out to your audience and customers. And as your customer base increases, your web-application evolves so that you can cater to their varying needs. But the more features you introduce in your application, the more requests and responses need to be handled by your applications. That, coupled with design (CSS) can make your web applications pretty bulky. You must be thinking, “So what! Most of my customers have access to high speed internet”. Well, according to a research conducted by Google, 53 percent of mobile users leave a site if it takes more than 3 seconds to load. That’s about the same time it took you to read the last sentence. So, you have to make sure that your website is light, and monitor it regularly to make sure the feature updates and the patch releases don’t create any loading or performance issues.

Yes, clients-side scripting (JavaScript) can come to your rescue, but using JavaScript and data-binding frameworks like Knockout.js may introduce a few challenges along with their perks.  In this article we would talk about how JavaScript libraries are triggered and the best synthetic monitoring approach for Knockout.js based web-application.


The Advent of JavaScript Libraries

A few decades ago, web-applications used to be simple. They would use HTML for the DOM, and bare minimum CSS. Any request from the client would be sent to the server, and a relevant response was sent back. Another way of putting it, to reflect a change on a DOM element, the whole page had to refresh. Given the limited bandwidth such requests could take up a lot of time. But after the introduction of JavaScript in 1995, everything changed.

Now, whenever a web page is loaded, few client-side scripting files (JavaScripts and libraries) are also sent along with the HTML and CSS. These scripts contain a set of actions which are user driven. Such libraries also allow the web application to send requests and receive responses to external APIs or web services using the HTTP protocol. JavaScript libraries are also used for AJAX calls and lazy loading of web applications.  These JavaScript features and other such libraries help your web application to utilize the network bandwidth more efficiently. It loads the bare minimum elements and design when the application loads, and then depending on users’ interactions and requests, these scripts and libraries trigger events to process or fetch data. So until you perform any action, the HTML rendering would be relatively static. But the moment you click on a button or any such action, the JavaScript event would be triggered to handle the request, making the application dynamic.


Knockout.js, Not Merely a Chip Off the Old Block

Knockout.js is just another client-side scripting framework, but its specialty is DOM manipulations. While other JavaScript frameworks attach to the complete DOM, Knockout.js binds to a specific DOM container of your choice. It is mostly used for web applications where the HTML structure is dynamic and is dictated by the users’ interactions. Some important features of Knockout.js include the following;

  • MVVM architecture.  The MVVM (Model – View – View Model ) architecture eases the creation of dynamic user interface. It helps to abstract the rendering logic from application logic.
  • Declarative binding.  Rather than writing code from scratch, Knockout.js allows you to embed data binding expressions in your HTML. This simplifies connecting UI parts to the data model.
  • Two-way data binding.  Two-way data binding between the data model and UI allows changes in the data model to immediately reflect on the UI, and vice-versa.


Ordinary Monitoring Techniques and Knockout.js Apps

To make sure any feature releases or bug fixes don’t hamper the performance of your applications, you must test and monitor the behavior of your web application regularly. You should monitor your application’s performance on your principal server, as well as on your mirror servers. You should also test its performance under heavy load (network traffic), to ensure the servers are able to handle such traffic.  Monitoring tools that rely on just the HTTP responses are missing the client-side responses.  Even if an HTTP response is successful, it doesn’t mean all the JavaScript files were executed and rendered by the browser.  The difference between when an application loads “completely” and when the user can interact with the application, can be several seconds. What HTTP monitoring techniques don’t account for are the dynamic entities in a web application. The responses to user interactions by a JavaScript, complex AJAX requests, API calls, and the loading of iFrames (while loading advertisements, depending on the content present).

For Knockout.js-based web applications that deal with real-time data binding with the DOM, the performance and the page load time would depend on a variety of user interactions and how the script processes the data provided by the user. For this reason, successful loading of the scripts alone is not a realistic means to monitor performance. There can be instances where the actual load time of a Knockout.js application can take several more seconds to trigger and load the dynamic modules of the DOM. Using ordinary monitoring techniques would give you faulty statistics and you won’t be able to perceive the application’s performance from the perspective of a real end user. This in turn can impact your business and ruin the user experience of your customer base. For such dynamic applications, we should use a bit more sophisticated approach.


Synthetic Monitoring and Knockout.js-based Web Applications

To find the actual performance from the user’s perspective and load time statistics for your Knockout.js-based webbapplication, you must find a way to monitor the load time of your applications and the time taken by the scripts to trigger the JavaScript events. The best way to do it is using synthetic monitoring to monitor dynamic elements.

  • Using real browsers to simulate user interaction.  Rather than using headless browsers for monitoring, use real browsers to simulate user interactions. This approach would account for the time taken by the browser driver to read and render the DOM and load the scripts in the present web page.
  • Record and replay user interactions to trigger JavaScript events.  Using a script recorder to script user interactions and replaying them, you can record the various user interactions, especially those that trigger the Knockout.js dependent DOM containers. So whenever the monitoring script runs on the server, it would load your web application on a real browser and perform the pre-recorded user interactions from different geo-locations. In this way your synthetic monitoring script would be able to take into account the server load time and the time it took to completely trigger the JavaScript events, giving you actual user performance results.
  • Content validation.  This is the most important validation when it comes to monitoring your dynamic web application.  Content validation is used to validate whether the JavaScript events have actually completed and the change is being reflected in the UI. Once the content validation is successful, it means all the requested changes and events have been triggered and completed. The time taken since the web application request was sent to the server, to the time it took to validate the content, reflects the true loading time and performance of your web application.  Generally the content can be text or image, depending on the type of DOM the Knockout.js script is bound to.



There have been great advancements in web application development techniques and strategies over the last decade. In order to ensure that your applications can continue to perform effectively, and meet the demands of your customers, you need an innovative solution that will support monitoring dynamic applications, web pages, and technologies like Knockout.js.  Dotcom-Monitor gives you the tools, like the EveryStep Web Recorder, and all the features you need to effortlessly monitor even the most complex web applications and websites.


Try the full Dotcom-Monitor platform free for 30 days.


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