Bootstrap is a CSS framework for building responsive websites, with an emphasis on being mobile-first. While there are other frontend presentation frameworks, Bootstrap is still the king of the hill in this arena—not only due to being the one with the most mind share, but it probably has the most runtime. What I mean by runtime is the number of times it's been used in websites, and thus it has been put through its paces more than the other CSS frameworks. Bootstrap's leading mind share (that is, popularity) is primarily due to three things:

• It was one of the very first frameworks of its kind (so the competition was virtually non-existent)
• It came with the backing of one of the top social websites in the world (that is, Twitter)
• It has been around since August 2011, and so is mature

Additionally, as we'll see in Chapter 8, Working with NG Bootstrap, the ng-bootstrap project is all about creating Angular widgets using Bootstrap 4, which says a lot about what the Angular community thinks of Bootstrap.

There is a reason that this third edition remains true to the relationship between Angular and Bootstrap, and that is because they are each leaders in their respective niches, as well as being symbiotically compatible and complimentary. In fact, these two frameworks are all you need to build the frontend part of powerful web applications—choosing just about anything you like for building out the backend, since all backend frameworks these days can produce and consume JSON, including mainframes still running COBOL programs. This is because JSON has become the most popular way to integrate systems through messaging.