How to correctly query elements in Shadow DOM with JavaScript selector?

Application of JavaScript Selector in Shadow DOM and FAQ

Shadow DOM is often a challenge when looking for page elements using JavaScript selectors. Shadow DOM is used to encapsulate the style and structure of components, improving code maintainability and reusability, but also increasing the complexity of element selectors. This article will explain how to effectively select elements inside Shadow DOM.

Problem: Selector failed

Many developers have problems selecting internal and external elements of Shadow DOM using document.querySelector . A common phenomenon is that the selector copied from external elements can only select external elements, and the query result of Shadow DOM internal elements is null; vice versa. This is because document.querySelector cannot penetrate Shadow DOM boundaries by default. Even if you indirectly get the shadowRoot object and query it, it may return null due to the selector path error or shadowRoot acquisition failed.

Solution: Correct access to Shadow DOM

The key to solving the problem is to understand element.shadowRoot property. document.querySelector cannot directly access Shadow DOM internal elements. You must first get shadowRoot of the target element, and then use querySelector to select it internally.

Here is a correct code example:

 const shadowHost = document.querySelector('ubisoft-connect'); // Get Shadow DOM host element if (shadowHost && shadowHost.shadowRoot) {
  const shadowRoot = shadowHost.shadowRoot;
  const targetElement = shadowRoot.querySelector('corresponding selector'); // Use querySelector in shadowRoot

  // Operation on targetElement} else {
  console.error('Shadow DOM host element does not exist or shadowRoot acquisition failed');
}

This code first gets the host element of the Shadow DOM (for example, ubisoft-connect ). It then checks if the host element exists and contains shadowRoot . Only when both are true can querySelector be used inside shadowRoot for element selection. Finally, if the acquisition fails, the error message is printed. Be sure to replace "对应的选择器" with the actual target element selector. This method ensures the robustness of the code and avoids errors caused by shadowRoot non-existence.

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