Understanding Mysterious Severe Performance Issues on Mobile Safari

Introduction

As a web developer, it’s always frustrating when our websites don’t perform as expected, especially on mobile devices. In this article, we’ll delve into a mysterious performance issue that was affecting a single webpage on an iPhone 5 running iOS 7. The problem was severe enough to make the browser unresponsive and even cause Safari controls to feel sluggish.

Background

The affected webpage is part of a larger responsive website with over 150 different UI pages. While both rendering and performance were fine on other devices, this particular page had been causing issues for months. We’ll explore what makes this page unique and how it differs from other pages on the site.

Page Overview

The problematic webpage is responsible for detecting the user’s current location, calculating sun times based on that location and date, and then rendering a table with sunset periods. The page relies on several external libraries and scripts, including the Suncalc JS library for calculating sun times.

Here’s a breakdown of what happens when you visit the webpage:

1. Location Detection: The system attempts to detect your current location using an alert prompt.
2. Sun Time Calculation: Based on your location and date, it calculates the sunset periods using the Suncalc JS library.
3. Table Rendering: It renders a table with colored background rows based on the calculated sun times.

Performance Issues

When visiting this webpage on Mobile Safari, users experience:

• Slow loading times (several seconds)
• Sluggish scrolling and navigation
• Unresponsive browser controls
• Occasional crash or freeze

The issue doesn’t seem to be related to animation, as the page’s visual rendering is minimal compared to other pages on the site. Furthermore, location detection is not a bottleneck, as users can manually input their location, and the system responds promptly.

Investigation

To better understand the root cause of this performance issue, we’ll investigate each step of the webpage’s functionality:

1. Location Detection: We’ve verified that the alert prompt for location sharing doesn’t cause any significant delays.
2. Sun Time Calculation: The Suncalc JS library is used to calculate sun times based on user input (location and date). This step seems like a likely candidate for the performance bottleneck.
3. Table Rendering: Although rendering a table with 12 rows and different background colors might seem resource-intensive, it’s unlikely to be the primary cause of this issue.

Conclusion

Based on our investigation, it appears that the Suncalc JS library is responsible for the severe performance issues experienced by users on Mobile Safari. While native JavaScript profilers are not available on iOS 7, we can use tools like the javascript_microrace() function to help identify performance bottlenecks.

Solution

To mitigate this issue, consider optimizing the Suncalc JS library’s calculations and rendering:

• Use debugger statements or print logs within your JavaScript code to help identify performance-critical sections.
• Optimize your location detection process by reducing unnecessary checks or using more efficient algorithms.
• Profile your application regularly to catch any new issues early on.

By understanding the root cause of this performance issue and implementing necessary optimizations, we can improve the overall user experience for our webpage.

Last modified on 2024-03-14