Planning Your Migration to Bootstrap 5

Migrating to Bootstrap 5 from an older version can feel like venturing into a maze of breaking changes, rewritten components, and reworked styling conventions. For many teams — especially those maintaining long-lived applications or inherited codebases — the instinct is to postpone the upgrade for “just one more release.” But with Bootstrap 3 and 4 end-of-life, the security risks and performance drawbacks of staying put can't be ignored forever. 

In this post, we’ll explore why moving to Bootstrap 5 is particularly time-intensive and challenging because of the major changes in the release. We'll also touch on how long-term support (LTS) can give teams more breathing room if they can't undertake the effort that a Bootstrap 5 migration requires. 

Why You Can't Ignore the Bootstrap 5 Migration

It’s always tempting to follow the mantra “if it ain’t broke, don’t fix it.” For those with applications built using older versions of Bootstrap (3 and 4), this is particularly enticing, as upgrading comes with some significant effort. However, staying on those older versions means that you’re relying on older and often outdated CSS (particularly for layout), and potentially outdated and vulnerable JavaScript libraries (such as older versions of jQuery).

When it comes to security, it’s not just outdated dependencies; it’s also the Bootstrap library itself. Since Bootstrap 3 reached end of life, over half a dozen CVEs have been disclosed against it; Bootstrap 4 has had a handful as well. Most of these are Cross-Site Scripting (XSS) vulnerabilities, which can lead to a number of negative outcomes including:

• Session hijacking, allowing an attacker to pose as another user
• Credential theft
• Data manipulation, tricking users into performing unexpected actions
• Malware delivery to your end users

How likely is it that your application is affected by these Bootstrap vulnerabilities? Consider this: two of these CVEs (CVE-2024-6484 & CVE-2024-6531) affect the very commonly used Carousel component of Bootstrap, while CVE-2024-6485 affects the button plugin. Chances are you are affected, unless you are using a commercial LTS version of Bootstrap.

Another thing to consider is the user experience. Bootstrap 3 and 4 both relied heavily on jQuery, which adds page loading overhead. Both are also using older CSS features that have modern, more performant equivalents today (e.g. CSS Grid outperforms Bootstrap 3’s float-based layouts, and is more consistent overall). Benchmarks show Bootstrap 5 having 30% faster page load times and 60% improvement in component performance over Bootstrap 4, with even greater differences reported against Bootstrap 3. 

One key part of these differences is that the older versions of Bootstrap supported older browsers, making it impossible for them to use modern CSS and JS features. This hampers performance and consistency of the Bootstrap components, which is then passed on as feature defects to your own users.

The bottom line is that you will eventually need to migrate your application eventually to address these security and performance issues.

Major Changes in Bootstrap 5

Every major version of Boostrap introduces significant changes, and generally there’s too many to list in an article such as this; the official Bootstrap 5 migration guide, which only covers from v4 to v5, is quite extensive. As such, I’ll cover just a few of the highlights here.

No More jQuery

At the time Bootstrap first burst onto the scene, jQuery was the dominant library used to interact with a web page’s document object model (DOM). It provided a ton of features to simplify manipulating, swapping, adding, and removing elements of a page that worked cross-browser, and which ironed out rough edges of the browser’s DOM API. Considering that Bootstrap was made to simplify common layouts and page structures, it made sense to utilize jQuery internally.

The other feature it provided was a unified API around making web requests, which made developing dynamic sites that pulled in content and/or data from web APIs simpler.

Since then, browsers and browser standards have made some enormous leaps in capabilities, particularly with the addition of web components, query selectors, and the fetch API. Most of what jQuery provided is now natively available with a common API across all major browsers, which means jQuery is superfluous.

Bootstrap 5 recognizes this, and drops the requirement for jQuery.

Of course, this has a knock-on effect: if you’ve been developing your own plugins or extensions to Bootstrap that were relying on jQuery, you are now faced with a choice: re-add jQuery to your dependencies and take the impact on page load and execution times, or rewrite your code to use the modern JS APIs. 

Revamped Grid and Layout System

While Bootstrap has always aimed for consistency in layout, older CSS technologies such as float and tables often were unpredictable between different browsers and even window sizes, and required a lot of testing even when using the framework to ensure they performed as expected.

As a result, in addition to the JavaScript changes represented by dropping the jQuery dependency, Bootstrap 5 has fully embraced modern CSS layout paradigms, such as Flexbox and Grid layouts. (To be fair, Bootstrap 4 adopted Flexbox as well, but pre-dated wide rollout of Grid.) These give better consistency, as well as better browser performance, which in turn makes development and maintenance easier, and is more likely to lead to better user experience.

Customization 

The other major change for developers is how you customize Bootstrap itself. Version 3 and prior used the venerable LESS CSS preprocessor; version 4 switched to SASS, which gave better performance and modularity, but meant major changes to how developers customize the framework. 

Bootstrap 5 switches fully to native CSS, using CSS custom properties to enable theming; it also uses native CSS media and capability queries, which speeds up execution dramatically. This approach means that theming is as simple as dropping an additional CSS file into your pages, and requires one less tool to understand and master in order to customize Bootstrap.

However, it also means another area to be concerned with migration, as you’ll have to adapt from LESS or SASS to vanilla CSS in order to migrate to Bootstrap 5. 

Redesigned Components and Class Names

This is where things change the most from version to version, and Bootstrap 5 introduces a ton of changes. The table below highlights some of the more impactful:

An Actual Bootstrap 5 Migration Story

When Bootstrap was first released as “Twitter Bootstrap”, open source projects were a targeted industry segment. OSS projects often need a web presence, but the developers producing them are often not designers or web developers. Bootstrap filled a gap for these projects, as it made it easy to create professional-looking project websites with very little effort.

In a previous role, I was project lead for Zend Framework, Zend’s OSS enterprise PHP framework, and have continued this role since transferring the project to the Linux Foundation as the Laminas Project. We adopted Bootstrap very early on, as it allowed my team to provide a solid, reusable design for our website, where we hosted our blog, releases, and documentation. I’ve also used it on a number of internal-facing websites, as these don’t require a dedicated design team. As such, I’ve overseen a few different version upgrades over the years.

Each upgrade required a major rewrite of the various sites’ markup. Many changes were infuriatingly difficult to identify:

• The class for toggling the state of a navbar was changed from “navbar-toggle” to “navbar-toggler” with version 4. A single character difference that totally changed behavior. On top of that, with version 5, we had to wrap the entire contents in an additional container, a scenario that’s easily overlooked.
• We’d made wide use of panels and wells in our Bootstrap 3 website. Migrating to version 4, we had to switch to cards and card decks and in version 5 we had to switch from card decks to grid columns. (Yes, it’s a better, more generic pattern, but was it easy to identify how to get the same behavior? No.)
• We’d used the jumbotron from the very beginning; with version 5, this component went away, and it took a while to understand how to accomplish the same effect using containers, background colors, and other components.
• Prior to version 5, form controls included input groups, which were used to group all markup for a given form element: labels, help text, the form control itself, validation messages, etc. It was a ton of markup, but it was predictable, and mostly didn’t change from version to version. And then version 5 came along, and, while vastly simplifying the markup, completely changed it as well — to the point that you essentially had to rewrite entire forms from scratch. This is fine for simple forms, such as a login form, or a newsletter email submission form, but for something more complex ­— for instance, something with dynamic elements, or multiple multi-selects and radio groups — the effort could take hours or days, and that’s just before testing.

Bottom line: These migrations are a massive time sink. The small sites took hours, the bigger sites took weeks, and ultimately you end up with something that looks and behaves exactly the same as it did before, albeit with better performance and security.

Many development teams will need to carefully consider when they can budget the time and resources to pull off a migration to Bootstrap 5. Having Bootstrap long-term support can be incredibly useful to maintain your site or application's functionality and cover your security/compliance bases until you are ready to migrate. 

The Case for a Full Bootstrap Rewrite

Honestly, even though it involves a lot of rewriting, the best option is to migrate, either to Bootstrap 5, or to vanilla CSS and JS. If you don’t have a design team or a team versed in modern CSS and/or JS, Bootstrap 5 is still an excellent choice, particularly because it’s fully embracing modern CSS and JS.

By migrating to version 5, you will move towards more semantic HTML. Sure, there’s still a lot of Bootstrap-specific markup and CSS classes, but the project is definitely moving towards simpler paradigms. I may have groused about the form changes, but here’s the part I didn’t mention: we had something like 50-60% less HTML markup with the version 5 code, and it was far less nested — instead of 3 to 4 layers of nested <div>s with multiple Bootstrap classes on each for each form element, we’d have 2 levels at most, with a single Bootstrap class in any given element. The examples look more like basic HTML forms than like DIV soup, and that’s a good thing.

This future-proofing of your application is a good thing as well. You may want Bootstrap as a crutch today, and potentially in the future. If there’s a version 6, migrating to it from version 5 will be easier than from 3 or 4. And if you decide later to strip out Bootstrap in favor of vanilla CSS or another design framework, there’s likely less work you need to do to make everything look decent, as the HTML you write for Bootstrap 5 is closer to semantic HTML than any previous Bootstrap version.

But here’s another reason to use Bootstrap, and other frameworks like it: they also provide important features you likely don’t think about, but which have outsized impact on your users. I’m talking about accessibility (a11y) in particular. Bootstrap attempts to implement and enable a11y guidelines and features, and does so in a way that is largely invisible to the developer, while “just working” for those who depend on the features. For places where a developer needs to provide them, all the examples in the documentation just include them, so for the developer who copies, pastes, and adapts examples, they’re likely implementing these features without even understanding why they exist.

So should you rewrite? Yes! It’ll prepare you for the future, help you streamline and reduce complexity in the markup for your website, improve performance and accessibility for your users, and help you provide better security. It’s a net win, even with the extra effort involved. And as already mentioned, getting Bootstrap LTS through a provider like OpenLogic means more time to test and get things right.

Final Thoughts

The migration to Bootstrap 5 introduces breaking changes across layout, components, JavaScript, customization, and theming, and in many cases requires completely rewriting markup you’ve relied on for years. But the payoff is significant: cleaner, more semantic HTML; better performance; modern CSS and JavaScript capabilities; improved accessibility baked in; and most importantly, a path forward that frees you from the technical debt of unsupported libraries.

Whether your goal is future-proofing, reducing page weight, eliminating jQuery, or closing security gaps, Bootstrap 5 represents a meaningful step forward. It's a step you'll definitely want to make at some point — but if you can't expend the time or team resources to execute it now, investing in Bootstrap LTS can bridge the gap. 

Additional Resources

• Datasheet - Bootstrap Long-Term Support
• Blog - Bootstrap Framework Basics
• Blog - New Bootstrap Vulnerabilities to Watch
• Blog - Using Bootstrap: Best Practices and Tips for Getting Started
• Blog - Introducing Bootstrap LTS From OpenLogic
• Blog: Top Open Source Frameworks from the State of Open Source Report