Web applications have evolved dramatically in complexity and functionality, often leveraging cutting-edge features such as custom elements to deliver a richer user experience. However, the varied landscape of browsers and devices can introduce unforeseen challenges in ensuring that these applications perform consistently across different environments. LambdaTest aids developers in verifying the compatibility and performance of their web applications on a myriad of browser-device combinations. When combined with Selenium, a renowned automation testing tool, LambdaTest empowers developers to create robust test cases that can validate custom elements seamlessly, providing confidence in an application’s cross-browser consistency and functionality. 

This article dives deep into the nuances of testing web applications with custom elements using LambdaTest, along with pertinent details. So, let’s jump in immediately…

What Are Custom Elements?

Custom Elements are a set of web platform APIs that allow you to define new types of HTML elements. They are a foundational aspect of Web Components, a suite of technologies that lets developers create reusable and encapsulated widgets or components for web applications. With Custom Elements, developers can create new kinds of HTML tags with behaviours and styles they define. Here’s a quick overview of the process of creating and using custom elements:

Defining A Custom Element: Custom elements should have a name that contains a hyphen to ensure they don’t conflict with existing or future HTML elements. For example: `<my-element></my-element>`.

JavaScript Class: Custom elements are defined by ES6 classes. This class defines the behaviour of the new element. For instance:

Extending Built-In Elements: Custom elements can also extend native HTML elements. For example, you could extend the standard button to add more functionality. This is done using the `extends` option during registration.

Attributes And Properties: Custom elements can have attributes and properties just like standard HTML elements, and you can define custom behaviours when these values change.

Challenges In Testing Custom Elements

Testing custom elements, as with many aspects of web development, presents its own set of challenges. These challenges often stem from the unique nature of Web Components and the encapsulation provided by the Shadow DOM. Here are some common challenges and considerations:

Shadow DOM Encapsulation: The Shadow DOM is designed to encapsulate styles and markup. This means accessing elements inside a Shadow DOM requires different techniques than traditional DOM querying. Many testing libraries might not natively support querying inside the Shadow DOM, making it more cumbersome to access and interact with these elements.

Lifecycle Timing: The lifecycle of a custom element (e.g., `connectedCallback`, `disconnectedCallback`) might not always align perfectly with the lifecycle of tests or the testing framework. Ensuring elements are fully upgraded (i.e., their custom element behaviours are attached) and ready for interaction before tests run can be tricky.

State And Propagation: Custom elements can have internal states that aren’t directly visible from the outside. This can make it challenging to set test conditions or verify results.

Event Handling: Custom events dispatched by custom elements may not always behave as native events, especially when it comes to propagation through the Shadow DOM boundary. This can make testing event handlers more complex.

Dependencies And Integration: Some custom elements might depend on other custom elements or third-party libraries. Ensuring that these dependencies are correctly loaded and initialized for testing is vital.

Cross-Browser Differences: While web components standards aim to be consistent across browsers, there are differences in implementations and support levels, especially in older or less common browsers. This might necessitate additional polyfills or workarounds, which in turn require testing.

Styling And Theming: Due to the encapsulation of Shadow DOM, verifying that styles are applied correctly can be challenging, especially when themes or external stylesheets are involved.

Mocking And Stubs: For isolated unit tests, you might need to mock some parts of the custom element behaviour or its dependencies. Creating mocks for custom elements or their internals (like the Shadow DOM) can be more challenging than for regular JavaScript modules.

Documentation And Best Practices: As the Web Components ecosystem is still growing and evolving, best practices and tools for testing can be less well-documented than those for more established frameworks or libraries.

Why Choose LambdaTest For Testing Custom Elements?

LambdaTest is an AI-powered test orchestration and test execution platform that can be particularly effective for testing custom elements and web components. Let’s delve into why LambdaTest can be a good choice and how it can simplify the testing process:

Cross-Browser Testing: LambdaTest offers a vast range of browsers and their versions available for automation testing. This is crucial when testing custom elements, as you need to ensure that your component behaves consistently across different browsers. In fact, you don’t need to worry about keeping browsers updated in your test environment; LambdaTest does that for you.

Parallel Testing: LambdaTest’s platform allows you to run multiple tests in parallel. This is especially beneficial when running tests across multiple browsers and devices, significantly reducing the total testing time.

Testing On Real Devices: While emulators can give an approximate idea, there’s no substitute for testing on real devices. LambdaTest provides access to a variety of real devices, ensuring that your custom elements perform well in real-world conditions.

Integrations With CI/CD Tools: LambdaTest can be integrated seamlessly with popular Continuous Integration and Continuous Deployment (CI/CD) tools. This ensures that testing custom elements can be a part of your regular development and deployment workflow.

Local Testing: LambdaTest offers a secure shell tunnelling feature that allows you to test web components and applications hosted on your local development environment. This is immensely helpful during the development phase when the changes haven’t been pushed to a public server.

Visual UI Testing: When dealing with custom elements, visual consistency across browsers is essential. LambdaTest offers screenshot testing and responsive testing across different browsers and resolutions. This ensures your custom elements look and feel the same everywhere.

Interactive Testing Sessions: LambdaTest allows you to interactively test your application. This is beneficial when troubleshooting specific issues with custom elements on particular browsers or devices.

Collaboration Features: If you discover an issue while testing, you can log it directly from the LambdaTest platform, and it integrates with many popular bug-tracking tools. This makes team collaboration more streamlined.

Automation Support: LambdaTest supports Selenium, so you can write automated tests for your custom elements and run them across the vast array of browsers and versions available on LambdaTest’s platform.

Scalability: Whether you’re a solo developer or part of a large team, LambdaTest scales with your needs. You don’t have to worry about infrastructure setup or maintenance, which is particularly helpful when dealing with a broad testing matrix for custom elements.

In essence, LambdaTest provides a comprehensive environment that addresses many of the challenges associated with testing custom elements. The platform’s flexibility, combined with its extensive browser and device coverage, ensures that custom elements are robust and consistent across all target platforms.

Testing Custom Elements With LambdaTest

Here is the full-fledged process of testing custom elements with LambdaTest. So, let’s go step by step:

Setting Up A LambdaTest Account

Visit the LambdaTest website. Click on the “Free Sign Up” or “Login” button. Follow the prompts to set up your account. Usually, this will involve providing your name, email, and setting a password. Once you’ve created your account and logged in, you’ll be taken to the LambdaTest dashboard.

Creating Test Environments

On the LambdaTest dashboard, navigate to the “Real-time Testing” section. Here, you can select the desired browser, its version, and the OS of your choice. Choosing relevant browsers and devices ensures that your custom elements function correctly across the different platforms your audience uses. Remember, not all browsers or versions will interpret custom elements in the same way. It’s imperative to test on a representative sample to catch and address inconsistencies.

Manual Testing Of Custom Elements

Manually testing your custom elements on LambdaTest is straightforward:

Launching A Test Environment: From the “Real-time Testing” section, after selecting your desired browser and OS, click “Start”. This will open a new browser instance with the selected configurations.

Navigating To Your Application: Enter the URL of the web application where your custom element resides. If your application is hosted locally, you need to use LambdaTest’s “Lambda Tunnel” feature to test it.

Inspecting Custom Elements: Use browser developer tools to inspect and interact with your custom elements, ensuring they behave as expected. If you need to take a screenshot, there’s a camera icon in the LambdaTest toolbar for this purpose.

Automated Testing Of Custom Elements

LambdaTest provides integration with Selenium, allowing you to write and run automated tests:

Setup: Install the required libraries for Selenium. If you’re using JavaScript, you might use `selenium-webdriver`.

LambdaTest Integration: You’ll replace `YOUR_LAMBDATEST_GRID_URL` with LambdaTest’s Selenium Grid URL and include your LambdaTest credentials. This allows you to run tests on LambdaTest’s infrastructure.

Running The Tests: Execute your test script, and it will run on the LambdaTest platform across the browsers and platforms you specify.

Visual Testing Of Custom Elements

Visual testing ensures that custom elements not only function correctly but also look consistent and as intended across various browsers and devices. Small visual inconsistencies can lead to a compromised user experience. Benefits of LambdaTest for visual testing:

Screenshot Testing: LambdaTest offers an automated screenshot feature. You provide a list of browsers, devices, and resolutions, and LambdaTest will capture screenshots of your custom element across all of them. This allows you to quickly spot visual inconsistencies.

Responsive Testing: Test how your custom elements render on different screen resolutions and sizes. LambdaTest provides a responsive testing tool where you can see how your custom element appears across multiple device resolutions simultaneously.

Smart Testing: LambdaTest’s AI can automatically detect visual regressions, making it easier to spot unintended changes or inconsistencies in your custom elements.


The world of web development is ever-evolving, with custom elements offering unique user experiences and personalizations. However, the diversity of devices, browsers, and platforms presents a formidable challenge for ensuring consistent and flawless performance. 

Utilizing platforms like LambdaTest, developers can efficiently tackle these challenges, running tests across numerous environments with ease. Embracing such robust tools is paramount not just for ensuring the fidelity of custom elements, but also for guaranteeing that users everywhere receive a seamless and high-quality web experience, regardless of their device or browser choice.