Internet buyers nowadays demand that sites load quickly, display well on any device and perform error free. When something going on feels somewhat wrong, such as buttons that do not work, web pages that load funny or sections of the webpage that appear broken they can just quit without making a purchase. This is the reason why the error-free experience and smooth user experience (UX) is such a significant feature to Shopify store owners.
Shopify provides a strong foundation for creating your store, but once you start using custom themes, installing apps, or modifying code, small errors can slip in. These issues often hide within CSS or JavaScript files and quietly affect site performance. Most of the time, you won’t notice them until customer interaction drops, bounce rates rise, or sales start falling—highlighting the importance of professional Shopify website design services to maintain a smooth and reliable user experience.
The good news is: these problems are easy to identify and resolve.. In this blog, we will demonstrate to you how to identify CSS and JS errors which might be damaging the user experience of your Shopify store. And regardless of whether you manage the store yourself or you interact with a developer to get your site up and running there are a few things to understand so that your site is kept in good health and so are your customers.
Understanding the Impact of Front-End Errors on UX
CSS and Javascript errors will not necessarily bring down your Shopify store, but they will invisibly trash user experience thereof. Broken photos, a fixed header that cannot be scrolled, or a checkout button that cannot be used to add a product to the cart can result in disappointment and frustrated sales.
Whenever users experience minor hustles in your site, their view on your brand wilts. Having technical problems are linked by people with unprofessionalism and that is a setback to trust. Your products might be the best but a bad UX will send people away. This is the reason Shopify Web Design should be made with performance and consistency in its mind.
To check these errors, research and coding should focus on clean functional front-end code in Shopify Website Design services. No matter where you are using a ready-made theme or Custom Shopify Website Design, improper edits, incompatibility with plugins, or missed updates may become the cause of the front-end errors.
Why does this matter?
- Poor UX reduces trust and credibility
- Errors may not show on all devices, making it hard to track
- Broken design affects mobile usability, harming SEO
- Slower loading times due to buggy scripts push customers awayeUsers bounce before completing a purchase, impacting your revenue
Common CSS & JS Issues in Shopify Stores
Let’s break down some of the most common errors found in Shopify front-end code and their potential consequences:
CSS Errors
- Overlapping content: Often caused by misused flexbox or grid layouts. Can block product information or images.
- Broken navigation menus: Navigation elements may appear out of place or disappear entirely on mobile.
- Improper text alignment or spacing: This makes content hard to read and unprofessional.
- Style conflicts from multiple apps or custom styles: When multiple apps inject conflicting stylesheets, it can break the entire layout.
JavaScript Errors
- Buttons not working (e.g., Add to Cart): Missing or broken event listeners in your JS can completely stop purchases.
- Sliders or carousels not loading: These UI elements are often critical for showcasing products but depend heavily on JS.
- Drop-downs not expanding: Important for product filters or navigation, drop-downs failing ruins UX.
- Forms not submitting: From contact forms to newsletter subscriptions, a broken form means lost leads.
These are often caused by conflicting scripts, missing code elements, or third-party apps that don’t integrate well with your theme. Without regular checks, these bugs can compound over time.
Tools to Detect CSS & JS Errors
1. Browser Developer Tools
- Open your store in Chrome or Firefox
- Press F12 to open Developer Tools
- Go to the “Console” tab to spot JS errors
- Use “Elements” and “Network” tabs to find CSS and load issues
- Real-time insights help you pinpoint exact line numbers for code issues
2. Lighthouse (Built into Chrome DevTools)
- Run performance audits from within DevTools
- Helps you see what’s slowing your site
- Flags accessibility issues, mobile responsiveness errors, and best practices
3. W3C CSS Validator
- Paste your CSS code or use your website link to find non-standard code
- Suggests changes based on industry standards for better browser compatibility
4. JS Hint / ESLint
- Analyze JavaScript code for syntax errors, bad practices, and bugs
- Great for maintaining clean, error-free custom scripts
If you’re not a developer, consider working with a Shopify web designer or Shopify web developer who understands how to properly run these audits and clean up the issues effectively.
Testing Your Shopify Store Across Devices
Testing Your Shopify Shop On Different Devices
It might look good on your desktop but fail on phone or tablets. This is why responsive testing plays an essential role in ensuring that the UX is consistent and interaction-friendly to all the users.
What to do:
- The Chrome DevTools device toolbar makes it possible to test different screen sizes
- BrowserStack or Responsinator: test devices and browsers, and operating system
- When possible test manually on actual devices, particularly iPhones and Androids
- Checkout flow, navigation, product zooms and pop-ups and so on
Responsive testing is a natural phase in development performed by Professional Shopify Website Designers. Good mobile experience can enhance both the UX as well as mobile SEO, as Google now implements mobile-first indexing.
How to Fix the Errors You Find
After identifying the issues, it’s time to fix them. Here’s how:
Fixing CSS Errors:
- Stick to theme standards: Avoid overriding classes unless necessary
- Use SCSS/LESS preprocessors: For better structure and reusability
- Clean redundant styles: Remove duplicate or unused CSS rules
- Use proper naming conventions and structure to avoid confusion
- Leverage media queries effectively for different screen sizes
Fixing JavaScript Errors:
- Ensure libraries load correctly: For example, jQuery must load before your scripts use it
- Avoid using multiple versions of the same library
- Check third-party app integrations: Ensure they aren’t clashing
- Use console logs and breakpoints to test JS functionality in smaller blocks
- Always test on staging before pushing changes live
When in doubt, hire Shopify experts—or better yet, a top Shopify developer—who can diagnose and resolve issues quickly without affecting other store functions.
Preventing Future CSS & JS Issues
The only right approach is to prevent the occurrence of errors at the initial stage. Here’s how:
Only rely on safe apps: Go with high-rated and well-supported apps
Duplicate theme testing: Before trying any major changes on a live theme, test those changes in a duplicate theme
Conduct code audits regularly: It would help to avoid big problems even with monthly checks
Collaborate with professional Shopify developers: they use best practices and well tested code
Automatize error checking: add plugins or services that will notify you when something goes wrong
To maintain your store bug free, secure and optimized, it is well worth investing into the Shopify Web Design ongoing services.
The Role of a Shopify Web Designer or Developer
The best Shopify website builders focus not just on appearance but also on optimizing every line of code for speed, usability, and device responsiveness. Their role extends beyond visual design—they optimize your store’s performance, mobile responsiveness, and script integrity. Partnering with top ecommerce specialists also brings in strategic know-how that improves conversions and long-term scalability.
What they do:
- Optimize front-end code to load faster and cleaner
- Implement responsive design for all devices
- Audit theme structure and app integrations
- Remove unused scripts and styles that slow down your site
- Provide ongoing support to fix bugs quickly
Before hiring, it’s important to understand the typical Shopify expert cost, which can vary depending on the complexity of your project and the level of customization needed. They write clean, modular code that’s easy to maintain and less prone to bugs compared to off-the-shelf themes.
Tips to Maintain Clean Code in Shopify
Here are some essential coding practices for long-term success:
- Use Git or version control: Always track your theme changes
- Document your custom code: For future edits or team collaboration
- Follow Shopify’s documentation: Use their best practices for app/theme structure
- Avoid multiple apps for the same function: Prevents script overload
- Minify CSS and JS files: Reduces page load times
- Test every feature after an update: Themes, apps, and scripts can break silently
Professional Shopify web design services often include code reviews, documentation, and backup management to keep your store safe and efficient.
Keep Your Shopify Store Bug-Free with Mandy Web Design
As a top-rated web design agency, Mandy Web Design develops and optimises Shopify stores, which provide an unmatched user experience. We optimize the speed of websites, make it look great, and convert more visitors by repairing invisible CSS and Javascript problems and designing your own, full-custom Shopify themes.
Why would you employ the services of Mandy Web Design?
- Professional Shopify Developers: We know how to deal with the complexity of front-end code and how a simple mistake can negatively affect performance.
- Clean, Search Engine Optimized Code: The code we write is clean, optimized and SEO friendly code and that will run faster and we will make sure it will stay stable longer.
- Theme Development: You need a new theme? Want to redesign the existing theme? We develop themes with precision.
- Mobile-First: We do testing on each device so that every visitor can receive the same high quality experience.
- Continued Guidance: As we continue to audit and check the performance, we eliminate the possibility of mishaps as they hit your shop.
FAQs About How to Catch CSS & JS Errors That Hurt Your Shopify UX
CSS-related problems, such as content overlapping, ruined layout, or bad mobile optimization, and JS problems, such as non-functional buttons or sliders, may develop an unpleasant customer journey and affect your sales.
The errors can be detected via browser developer tools (F12), or Chrome Lighthouse audits, or such services as W3C Validator or JS Lint. Such instruments show what is not working and why it is slowing you up or ruining your UX.
Yes. An error in the “Add to Cart” or Checkout button because of JS can bring the buying process to a full stop and cause loss of revenue.
A majority of people make purchases through mobiles. In case you fail to optimize your site, errors can occur only on mobile devices or tablets and destroy your SEO and alienate potential clients.
We detect and mend the invisible CSS and JS bugs, optimize the codes and make your store more speedy, responsive as well as pleasing to the eyes across all devices.
Yes. Mandy Web Design is one of the experts in creating a fully custom Shopify theme to meet your company brand, performance requirements, and customer experience strategy.
Absolutely. Any design that we create is compatible with all types of devices making it run smoothly on smartphones, tablets, and desktops.
Our performance auditing is done continuously, theme patches and bug fixes are applied continuously, and we ensure that your store remains secure, optimized and runs efficiently, even beyond launch.
About the Writer
Mandeep Singh Chahal
Founder/CEO, Mandy Web Design
Mandeep Singh Chahal is the proud Founder/CEO of Mandy Web Design. After completing his graduation from Punjab University, Mr. Mandeep started gaining experience in SEO, Digital Marketing, Web Designing, and Business Development. His years of experience have earned him a reputed Web Design Company – Mandy Web Design.