On the fourth birthday of the first release, the Bootstrap team has announced the alpha release of version 4.
In a blog post, Bootstrap creator Mark Otto laid out the major changes. He said that v4 is a "massive undertaking that touches nearly every line of code."
The first three versions of Bootstrap used Less for CSS, but version 4 swaps out Less in favor of Sass. According to Otto, there were a few reasons for the switch:
- Sass has a larger community of developers. - Sass seems to be iterating as a tool faster than Less. - Sass is really similar to Less, so it's an easier transition to make than jumping right to PostCSS. - LibSass (the C implementation of the traditional Ruby Sass) is super fast, faster than Less in my casual tests).
With an eye to the future, version 4 now supports flexbox. Given the awkward state of flexbox browser support, it isn't enabled by default. Another major change is the switch from px units to rem and em units where appropriate. The rem unit sizes elements based on their relative size to the top-level html element. On the JavaScript side, all JavaScript plugins have been rewritten in ES6.
Developers that still need IE8 support have to stay on version 3 as version 4 drops support for the browser. A migration guide is available to give developers more details on what else has changed.
Also announced is the availability of Bootstrap Themes. While developers can tweak the design of an app built with Bootstrap, a common complaint was that apps tended to look the same. Low cost themes have been available at sellers like Themeforest for years, but the new gallery contains three official themes that are fully supported. Each costs $99 and includes free updates for the life of the theme. While all the current themes are for Bootstrap 3, many will be updated for version 4.
There's no release date set for v4. Otto said in his post that before the final release, we'll see a few alpha releases, two betas, and two RCs. Developers can take part in development at the GitHub repository and chat with the creators and community in the Bootstrap Slack channel.