CWV-MOBILE Optimize Critical Path Rendering For AEM Sites

Core Web Vitals (CWV) are crucial for delivering a seamless user experience, especially on mobile devices. A slow-loading page can lead to user frustration and higher bounce rates. This article dives into the specifics of optimizing Critical Path Rendering (CPR) for a website built on Adobe Experience Manager (AEM) Sites, focusing on a real-world performance issue and its resolution. We'll explore the problem, the proposed solution, and the implementation details, providing actionable insights for developers and website owners looking to enhance their mobile performance.

Understanding the Core Web Vitals Performance Issue

The core web vitals are a set of metrics that Google uses to measure user experience. These metrics include Largest Contentful Paint (LCP), First Input Delay (FID), and Cumulative Layout Shift (CLS). In this case, the focus is on LCP, which measures the time it takes for the largest content element on a page to become visible. A high LCP can significantly impact user experience, making the page feel slow and unresponsive. Guys, let's get into the details, yeah?

The Challenge: Slow LCP on Mobile

The URL https://add-cwv-check--bbird--aemsites.aem.page/ was flagged for a high LCP on mobile devices. This means that the largest content element on the page was taking too long to load, leading to a poor user experience. The priority for this issue was set to high, indicating the urgency of addressing it. The expected impact of the optimization was a 300-500ms reduction in LCP, a substantial improvement that can make a noticeable difference in page load times. Let's understand what's really up, alright?

Diving into the Details: The Root Cause

The description of the issue pointed to the root cause: the LCP element was taking too long to load. This often happens when critical resources are delayed, preventing the browser from rendering the main content quickly. The category of the issue was identified as JavaScript, indicating that JavaScript-related optimizations were likely the key to solving the problem. Now, let's break this down a bit more, shall we?

The Proposed Solution: Deferring Non-Critical Scripts

To address the slow LCP, the proposed solution involves optimizing the critical rendering path by deferring non-critical third-party scripts. This means that scripts that are not essential for the initial rendering of the page should be loaded later, allowing the browser to prioritize the resources needed for the LCP element. Specifically, the implementation details suggest moving auth0-spa-js.production.js to load in the delayed phase. This script, likely related to authentication, is not critical for the initial rendering and can be loaded asynchronously without blocking the main thread. Understanding the critical rendering path is crucial, so let's dive a little deeper into that, alright?

Critical Rendering Path: The Key to Performance

The critical rendering path is the sequence of steps the browser takes to render a webpage. It involves parsing HTML, constructing the DOM (Document Object Model), parsing CSS, constructing the CSSOM (CSS Object Model), combining DOM and CSSOM to create the render tree, calculating the layout, and finally, painting the pixels on the screen. Any resource that blocks this path can delay the rendering of the page. By deferring non-critical scripts, we ensure that the browser can focus on the essential resources needed to render the LCP element quickly.

Implementing the Optimization Strategy

The implementation details provide a clear roadmap for addressing the performance issue. By deferring non-critical scripts, particularly auth0-spa-js.production.js, we can significantly improve the LCP. This involves modifying the way the script is loaded, ensuring it doesn't block the initial rendering of the page. Let's break down the steps involved in this implementation, yeah?

Step-by-Step Guide to Implementation

1. Identify Non-Critical Scripts: The first step is to identify all the scripts that are not essential for the initial rendering of the page. This often includes third-party scripts, analytics scripts, and scripts related to non-critical features.
2. Defer Scripts: There are several ways to defer scripts. One common method is to use the defer attribute in the <script> tag. This tells the browser to download the script in the background and execute it after the HTML parsing is complete. Another approach is to load the script asynchronously using the async attribute, which downloads the script in the background and executes it as soon as it's available.
3. Move Scripts to the Delayed Phase: In this specific case, the implementation details suggest moving auth0-spa-js.production.js to the delayed phase. This likely involves loading the script in a separate JavaScript file or using a dedicated script loading mechanism.
4. Test Thoroughly: After implementing the changes, it's crucial to test the website thoroughly to ensure that the optimizations have the desired effect and that no functionality is broken. Use tools like Google PageSpeed Insights and WebPageTest to measure the LCP and other performance metrics.

Copilot Implementation Request: A Detailed Analysis

The Copilot Implementation Request provides a comprehensive set of instructions for an AI assistant to analyze and optimize the website. This request outlines the performance target, priority, effort, device focus, and URL tested, giving Copilot a clear understanding of the task at hand. Now, let's see what Copilot is up to, alright?

Key Focus Areas for JavaScript Optimization

The request highlights several focus areas for JavaScript optimization, including:

1. File Locations: Copilot is instructed to look for JavaScript files in specific directories, such as /scripts/, /blocks/, /libs/, /head.js, and /delayed.js. This helps Copilot narrow down the search and focus on the most relevant files.
2. Render-Blocking Scripts: Identifying render-blocking scripts is crucial for optimizing the critical rendering path. Copilot is asked to identify these scripts and implement code splitting to reduce their impact.
3. Async and Defer Attributes: Adding async or defer attributes to scripts can significantly improve performance. Copilot is instructed to apply these attributes where appropriate.
4. Unused Code and Dependencies: Removing unused JavaScript code and dependencies can reduce the overall size of the JavaScript files, leading to faster download and execution times.
5. Lazy Loading: Implementing lazy loading for non-critical JavaScript ensures that these scripts are only loaded when needed, further optimizing the initial page load.
6. AEM Edge Delivery: For AEM Edge Delivery projects, Copilot is instructed to check /scripts/scripts.js for optimization opportunities.

Implementation Strategy and Expected Outcome

The implementation strategy reinforces the need to defer non-critical third-party scripts and move auth0-spa-js.production.js to the delayed phase. The expected outcome is a 300-500ms reduction in LCP and better mobile performance. This aligns with the initial performance target and provides a clear goal for the optimization efforts. Alright, we've got a clear goal here, let's see how we can achieve it.

AEM Edge Delivery Context: Best Practices and Considerations

The AEM Edge Delivery Context is crucial for ensuring that the optimizations are compatible with the platform's architecture and conventions. AEM Edge Delivery Services projects follow specific patterns and best practices, which must be considered during the optimization process. So, what are the best practices here, huh?

Key Considerations for AEM Edge Delivery

1. Follow AEM EDS Patterns and Conventions: Adhering to AEM EDS patterns and conventions ensures that the optimizations are maintainable and compatible with future updates.
2. Maintain Block-Based Architecture: AEM uses a block-based architecture, where content is structured into reusable blocks. The optimizations should not break this architecture and should maintain the modularity of the content.
3. Compatibility with Franklin/Helix Pipeline: AEM Edge Delivery relies on the Franklin/Helix pipeline for content delivery. The optimizations should be compatible with this pipeline and should not introduce any performance bottlenecks.
4. Impact on Author and Publish Environments: The optimizations should be considered for both the author and publish environments. Changes in one environment can impact the other, so it's essential to test the optimizations in both contexts.

Creating a Focused PR: The Final Step

The final step in the optimization process is to create a focused Pull Request (PR) that addresses the specific performance issue. This PR should include clear before/after metrics, demonstrating the impact of the optimizations. A well-documented PR makes it easier for reviewers to understand the changes and ensures that the optimizations are properly implemented. Let's wrap this up with a nice and tidy PR, alright?

Essential Elements of a Focused PR

1. Clear Description: The PR should have a clear description of the performance issue and the optimizations implemented.
2. Before/After Metrics: Include metrics that demonstrate the impact of the optimizations. This can include LCP, First Contentful Paint (FCP), and other performance metrics.
3. Code Changes: Clearly highlight the code changes made to implement the optimizations.
4. Testing Results: Include the results of any testing performed to validate the optimizations.
5. Documentation: Provide any necessary documentation or explanations for the changes.

Conclusion: Optimizing for Mobile Performance

Optimizing Critical Path Rendering is crucial for delivering a fast and responsive mobile experience. By deferring non-critical scripts, optimizing JavaScript, and following AEM Edge Delivery best practices, developers can significantly improve LCP and other performance metrics. This article has provided a detailed overview of the process, from identifying the performance issue to implementing the optimizations and creating a focused PR. By following these guidelines, you can ensure that your website delivers a seamless experience for your users. So, let's get out there and make those websites fly, guys!