On January 31, 2012, Bootstrap 2 was released, which added built-in support for Glyphicons, several new components, as well as changes to many of the existing components. This version supports responsive web design, meaning the layout of web pages adjusts dynamically, taking into account the characteristics of the device used (whether desktop, tablet, or mobile phone).
On August 19, 2013, Bootstrap 3, was released. It redesigned components to use flat design and a mobile first approach. Bootstrap 3 features new plugin system with namespaced events. Bootstrap 3 dropped Internet Explorer 7 and Firefox 3.6 support, but there is an optional polyfil for these browsers.
Mark Otto announced Bootstrap 4 on October 29, 2014. The first alpha version of Bootstrap 4 was released on August 19, 2015. The first beta version was released on August 10, 2017. Mark suspended work on Bootstrap 3 on September 6, 2016, to free up time to work on Bootstrap 4. Bootstrap 4 was finalized on January 18, 2018.
Significant changes include:
- Major rewrite of the code
- Replacing Less with Sass
- Addition of
Reboot, a collection of element-specific CSS changes in a single file, based on
- Dropping support for IE8, IE9, and iOS 6
- CSS Flexible Box support
- Adding navigation customization options
- Adding responsive spacing and sizing utilities
- Switching from the pixels unit in CSS to root ems
- Increasing global font size from 14px to 16px for enhanced readability
- Dropping the
- Dropping the
- Huge number of utility classes
- Improved form styling, buttons, drop-down menus, media objects and image classes
Bootstrap 4 supports the latest versions of the Google Chrome, Firefox, Internet Explorer, Opera, and Safari (except on Windows). It additionally supports back to IE10 and the latest Firefox Extended Support Release (ESR).
Bootstrap 5 was officially released on May 5, 2021.
Major changes include:
- New offcanvas menu component
- Rewriting the grid to support columns placed outside of rows and responsive gutters
- Migrating the documentation from Jekyll to Hugo
- Dropping support for IE10 and IE11
- Moving testing infrastructure from QUnit to Jasmine
- Adding custom set of SVG icons
- Adding CSS custom properties
- Improved API
- Enhanced grid system
- Improved customizing docs
- Updated forms
- RTL support