How to Reduce Largest Contentful Paint (LCP) on Mobile for Shopify's Dawn Theme

By Tony Ng.
June 23rd, 2024

How to Reduce LCP on Mobile for Shopify's Dawn Theme

Introduction

Improving your website's performance is crucial for enhancing user experience and ensuring higher conversion rates. One of the most significant metrics to focus on is Largest Contentful Paint (LCP), especially on mobile devices. Let's explore how to effectively reduce LCP on mobile while using Shopify's Dawn Theme.

Understanding LCP

What is LCP?

Largest Contentful Paint (LCP) measures how long it takes for the largest content element in the viewport to become visible. Ideally, this should happen within 2.5 seconds for a good user experience.

Why is LCP Important?

LCP is a critical factor in the Core Web Vitals, which affect your site's SEO ranking and user satisfaction. High LCP times can lead to reduced user engagement and higher bounce rates.

Identifying the Problem

Possible Causes of High LCP

Unoptimized Images: Large or poorly optimized images can significantly slow down loading time.
Render-Blocking Resources: JavaScript and CSS can delay the rendering of the page.
Server Response Times: Slow server responses can increase LCP.
Client-Side Rendering: Heavy client-side rendering tasks can also be a bottleneck.

Solutions to Reduce LCP

Step 1: Optimize Your Images

Compress Images: Use tools to compress your images without losing quality.
Lazy Load Images: Load images only when they appear in the viewport.

Step 2: Defer or Async JavaScript

What are Defer and Async?

Defer: Scripts with the defer attribute will only execute after the HTML document has been fully parsed.
Async: Scripts with the async attribute will execute as soon as they are available without blocking the HTML parsing.

Implementing Defer and Async in Shopify

Find and Identify Render-Blocking Scripts: Locate scripts that are blocking the rendering of your page.
Modify the Script Tags

<script defer src="your-script.js"></script>
<script async src="your-script.js"></script>

Adding to Dawn Theme

Navigate to Theme Editor
Locate JavaScript Files: Usually found in the <head> section of theme.liquid
Insert Defer or Async Attributes: Modify the script tags accordingly.

Step 3: CSS Optimization

Minify CSS Files: Reduce the size of your CSS files.
Remove Unused CSS: Clean up any unused CSS to speed up loading time.

Step 4: Improve Server Response Times

Use a Content Delivery Network (CDN): This helps in reducing latency.
Optimize Server Performance: Ensure your server is optimized for speed.

Step 5: Client-Side Rendering Optimization

Code Splitting: Break down your JavaScript code into smaller pieces.
Optimize Third-Party Scripts: Remove or delay unnecessary third-party scripts.

Common Questions

1. How do I measure LCP?

You can measure LCP using tools like Google PageSpeed Insights or Lighthouse. These tools will provide insights and suggestions for improving LCP.

2. Is the Dawn theme inherently slow?

No, the Dawn theme is generally well-optimized. However, specific issues related to your setup or customizations might be affecting performance.

Conclusion

Reducing LCP on mobile for Shopify's Dawn theme is critical for enhancing user experience and improving SEO. By optimizing images, deferring or asyncing JavaScript, and following the best practices for rendering and server performance, you can achieve a significant improvement in LCP. While some solutions may require professional help, the steps outlined above can serve as a solid starting point for anyone willing to dive into the technical aspects of web performance optimization.