Test Automation Blog: ShadowDOM and its handling with Selenium

ShadowDOM

Shadow DOM is a technique used in web development to encapsulate the styling and behavior of a component within its own private DOM tree, separate from the main document DOM tree. It allows developers to create custom elements that can be reused across different web pages or applications, without worrying about the element's styling or behavior interfering with other elements on the page.

When a web component is created using Shadow DOM, the component's internal structure and styling are hidden from the rest of the page. The component can still interact with the rest of the page, but the rest of the page cannot interact with the component's internal structure or styling. This helps to prevent styling conflicts and unintended side effects, and allows components to be easily reused without modification.

The Shadow DOM tree is structured similarly to the regular DOM tree, with elements and nodes arranged in a hierarchical fashion. The main difference is that the Shadow DOM tree is encapsulated within a "shadow host" element in the regular DOM tree, and is not directly accessible or modifiable from outside of the shadow host.

Shadow DOM is widely used in modern web development, and is supported by most modern web browsers, including Chrome, Firefox, and Safari. It is commonly used in conjunction with other web technologies, such as Custom Elements and Web Components, to create reusable UI components and widgets.

Here is an example diagram of a Shadow DOM tree:

In this above example, we have a regular DOM tree that contains a <my-shadow-host> element, which is a web component that uses Shadow DOM to encapsulate its internal structure and styling. The Shadow DOM tree is contained within the #shadow-root element of the Shadow host, and contains two child elements: <my-shadow-element> and <my-other-element>. These elements are encapsulated within the Shadow DOM tree and cannot be accessed directly from the regular DOM tree.

Outside of the Shadow host, we also have a regular DOM element called <regular-element>, which is not part of the Shadow DOM tree and can be accessed directly using standard DOM manipulation techniques.

Handling ShadowDOM with Selenium

In Selenium with Java, you can interact with Shadow DOM elements on a webpage using the WebDriver API. However, since Shadow DOM elements are encapsulated within their own DOM tree, they cannot be accessed directly using the standard WebDriver methods such as findElement or findElements. To interact with Shadow DOM elements in Selenium with Java, you will need to use the executeScript method of the JavascriptExecutor interface to execute JavaScript code that can access the Shadow DOM tree and find the desired elements. Here is an example of how to access a Shadow DOM element using Selenium with Java:

// Find the Shadow host element WebElement shadowHost = driver.findElement(By.cssSelector("my-shadow-host")); // Execute JavaScript to access the Shadow DOM tree WebElement shadowRoot = (WebElement) ((JavascriptExecutor)driver).executeScript("return arguments[0].shadowRoot", shadowHost); // Find the element within the Shadow DOM tree WebElement shadowElement = shadowRoot.findElement(By.cssSelector("my-shadow-element")); // Interact with the Shadow DOM element shadowElement.click();

In this example, my-shadow-host and my-shadow-element are CSS selectors that identify the Shadow host and Shadow element, respectively. The executeScript method is used to execute JavaScript that accesses the Shadow DOM tree and returns the desired element. Once the Shadow element is located, you can interact with it using standard WebDriver methods.

Test Automation Blog

Sunday, 19 February 2023

ShadowDOM and its handling with Selenium

ShadowDOM

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