--- title: "Detect when Nutrient PDF viewer UI loads | Nutrient" canonical_url: "https://www.nutrient.io/guides/web/knowledge-base/detect-pspdfkit-ui-loaded/" md_url: "https://www.nutrient.io/guides/web/knowledge-base/detect-pspdfkit-ui-loaded.md" last_updated: "2026-05-18T14:28:53.388Z" description: "Learn to detect when the Nutrient UI loads in the Web SDK using `renderPageCallback` and `MutationObserver` for effective application configuration." --- When working with Nutrient Web SDK, you may need to detect when the UI has fully loaded to determine setting some configurations in your application accordingly. ## Proposed suggestion While we don’t have a specific event for UI loading completion, there are two effective approaches to detect when the UI has loaded, outlined below. 1. Using [`renderPageCallback`](https://www.nutrient.io/api/web/interfaces/Configuration.html#renderpagecallback): ```javascript let globalInstance; NutrientViewer.load({...baseOptions, renderPageCallback: function (ctx, pageIndex, pageSize) { if (pageIndex === globalInstance.totalPageCount - 1) { alert("last page loaded"); } } }).then((instance) => { globalInstance = instance; }); ``` - This method lets you know when each page has been rendered. 2. Using a `MutationObserver`: ```javascript function attachPageLoadObserver() { const pageClassSelector = 'PSPDFKit-Page' // Select the entire DOM for observing: const target = document.querySelector('body'); // Create a new observer instance: const observer = new MutationObserver(function() { if (document.getElementsByClassName(pageClassSelector)) { console.log("Page loaded!"); // Do something... observer.disconnect(); } }); // Start the observer. observer.observe(target, { childList: true }); } … attachPageLoadObserver() … ``` - This approach listens for changes in the DOM, specifically for the addition of elements with the `PSPDFKit-Page` class. - It’s a more general method that doesn’t rely on Nutrient-specific APIs. ## Choosing the right approach - Use `renderPageCallback` if you need to know when specific pages are rendered or if you prefer using Nutrient’s built-in APIs. - Use the `MutationObserver` approach if you want a more general solution that doesn’t depend on Nutrient-specific callbacks. ## Summary While Nutrient Web SDK doesn’t provide a direct event for UI loading completion, you can use either the `renderPageCallback` or a `MutationObserver` to detect when the UI has loaded. Choose the method that best fits your specific use case and application architecture. Remember to test your implementation thoroughly to ensure it works consistently across different documents and loading scenarios. If you need further assistance or have questions about detecting UI loading in Nutrient Web SDK, don’t hesitate to [reach out](https://support.nutrient.io/hc/en-us/requests/new) to the Nutrient Support team. --- ## Related pages - [Add Custom Keyboard Shortcuts](/guides/web/knowledge-base/add-custom-keyboard-shortcuts.md) - [How to add a custom toolbar item to display current zoom percentage](/guides/web/knowledge-base/add-custom-zoom-perentage.md) - [Add Listener Text Note Annotation](/guides/web/knowledge-base/add-listener-text-note-annotation.md) - [Add Listener Toolbar Item](/guides/web/knowledge-base/add-listener-toolbar-item.md) - [Add Signature Initials](/guides/web/knowledge-base/add-signature-initials.md) - [Listen to an annotation’s hover event](/guides/web/knowledge-base/annotations-hover-event.md) - [Blurry Print Resolution](/guides/web/knowledge-base/blurry-print-resolution.md) - [Automatic Annotation Field Tab Ordering](/guides/web/knowledge-base/automatic-annotation-field-tab-ordering.md) - 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