React.js, colloquially known as just React, is an open-source JavaScript library published and maintained by Facebook used to build dynamic user interfaces for single-page applications (SPAs) and modern web applications. It is a lightweight front-end library capable of handling client-side operations of websites and mobile applications. Jordan Walke designed the tool while being a software engineer at Facebook. He got inspiration from XHP, an HTML component library for PHP. The library was first released as FaxJS in 2011 on Facebook’s News Feed, but was not deployed open-source until May 2013.

React’s main goal is to be easy to use, fast to develop with and scalable over time. It builds an in-memory representation of the web browser’s DOM (Document Object Model) to manage front-end operations. This allows developers to design views for every state in their applications while it efficiently renders reusable UI components with updated data every time there is a change. Since React operates on a virtual DOM, it manipulates data changes much faster than if it accessed the browser’s DOM directly.

Nonetheless, despite the clever techniques React has to reduce the amount of heavy DOM operations to quicken component rendering, in most cases, it will not be enough to optimize application performance. Developers must take a step further to guarantee modern day expectations by using adequate practices and reliable monitoring tools.


Why does Load Testing Applications Matter?

The success of today’s websites and web applications is significantly influenced by how clean and smooth their user experience is. Modern apps live in an extremely competitive market where only those who can efficiently reduce their load time and optimize their performance can retain an increase in user engagement. To put the importance of the matter into perspective, the BBC’s new portal lost around 10 percent of user engagement for every additional second the website took to load. In another study, DoubleClick by Google found that websites that loaded within 5 seconds had 70 percent longer sessions and an overall better user engagement than websites that took almost four times as long.

Slow applications may be victims of poorly written code, resource bottlenecks and ultimately, poor planning and maintenance. Therefore, it is pivotal for developers to conduct performance tests and constant monitoring on their applications to determine which area of their system’s architecture needs attention and take the adequate actions to mitigate the issue. Addressing the issue efficiently will result in offering users a smoother user experience.


Native Tools to Improve Load Times

Let us look at some well-known tools to monitor and optimize load times and overall performance of React applications.

React Developer Tools

The React Developer Tools is a developer extension available for Chrome, Firefox, and as a standalone app that allows developers to inspect a React application’s component hierarchy and record performance information. The extension offers a profiler plugin that consumes React’s Profiler API to gather information about every component rendered in the application and committed to the DOM in order to diagnose performance issues. Then, the Profiler groups these commits to show performance info.

Developers are able to filter their app’s commits from a session among various charts that represent performance data. These charts can filter the recorded performance data by components, by interactions and by rendering time.

Using React’s Perf

Perf is React’s code-based profiling tool. It is an add-on library developers can use in development mode diagnose the overall performance of their applications. It is used to log measures like mount and render time of specific components. The library consists of three main methods to collect data and six others to print it to the console. The start() and stop() methods determine the beginning and the end of the performance session. All operations done in between are recorded and measured.  The react-addons-perf tool is no longer supported from React 16 onwards.

Chrome Development Tools

The Chrome Development Tools are a set web developer utilities included in the Google Chrome web browser that help developers from all web development technologies quickly edit web pages and visualize its changes, and diagnose problems with its debugging tools at runtime to build better websites. In the case of React applications, the Development Tool’s Performance tab helps distinguish which components are loading and how long it takes for them to render.

The Performance tab works similarly as the React’s Profiling extension. It records the performance of an application from a point set by the developer. After fully loading the page or stopping the performance recording, the data published to the User Timing API can help React developers see the computation time of each component. Additionally, it shows every JavaScript function call, which is very useful to diagnose why a specific component might take a long time to load.


LoadView’s Approach to Optimize React Application Performance

LoadView takes the stakes higher by utilizing the EveryStep Web Recorder, a powerful scripting tool that simulates client-side operations with websites and applications to test complex user paths and scenarios. The EveryStep Web Recorder is capable of capturing complex interactions like mouse clicks, hovers, and movements, image and text verification, menu selections and much more. Moreover, testers can load custom data to simulate the same actions from multiple users such as account log-ins, sorting and filtering information, or test dynamic behaviors. Developers can dive deeper into the tests and manually edit the performance script using C# to automate the execution of repetitive tasks within then application.

EveryStep Airbnb


LoadView’s EveryStep Web Recorder offers React Developers the capacity to inspect deeply into their app’s components rendering time along with every operation hidden to the user’s eyes. Waterfall charts and performance reports capture overlooked interactions in the DOM that can cause function calls to external sources and measure overall response times.

waterfall chart


Load Testing Applications Written in React.js: Conclusion

React is one of today’s most on-demand front-end development tools. Its component-based development structure reduces development time and proposes the chance for developers to reuse code in an efficient manner. However, it is not enough to rely on the library’s fast execution time. Development teams must use performance-monitoring tools like React DevTools to successfully identify performance issues and take proper actions to optimize their applications, and LoadView’s EveryStep Web Recorder to accurately replicate user paths and scenarios to diagnose hidden tasks that can potentially be slackening app response time and deteriorating user experience.  You can try the EveryStep Recorder right now to start scripting user actions within your React applications and upload them for load testing within the LoadView platform.

Sign up for the LoadView free trial and get $20 in load testing credits to get started today!