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Bower is flexible enough that you can manage pretty much any package you would need on the front-end, so you can manage all your dependencies with one tool, including CSS, boilerplate, fonts and more.
Pro Largest front-end specific package registry
Pro Easily integrates with other tools
Because of Bower's focus on simplicity, it makes it much easier to integrate with other tools, so it has a wide range of support with workflow wrappers and task managers such as yeoman and grunt.
Pro Simplicity provides more flexibility
Bower doesn't try to handle too much of the workflow process, which means it's more flexible, and can be incorporated into more workflows. It tries to just do package management well and nothing else, which is why so many workflow wrappers support it. Because it doesn't try to do too much vertical integration, it also means that the list of supported components that it manages is huge.
Pro Requires a flat dependency tree
While nested dependencies are better for backend modules that need lots of inter-dependency, they lead to bloated file sizes. Flat dependencies are better for frontend optimization, where file size needs to be more closely managed.
Pro Does not store components in a registry
You always get package directly from owner's repository, i.e. you will always get latest version as soon as its version tag is committed without need of waiting until owner publishes updated package.
Pro Simpler to manage varied code
Because Bower makes few assumptions about the source and format of packages, it's easier to apply it to more of your packages
Pro AMD & CJS compatible
Bower strives to be as simple of a package manager as possible and puts as few restrictions on the packages in the registry as possible, making it the most flexible package manager with the most potential packages.
Con Does not store components in a registry
Bower installs components directly from urls and repositories, which makes it more susceptible to components being taken down, with fewer guarantees about their availability.
Con Seems like a redundant package manger
NPM with Webpack/Browserify can handle all the dependencies for both back-end and front-end. The only place where Bower may be useful is for projects which use libraries not supported by NPM, such as Polymer.
Con Difficult to create bundles
To create a minified bundle of all the required JS dependencies other tools need to be used.
Con Lack of signing of packages on the repository
Anyone can register their package on Bower's GIT registry - on one side, this brings a lot of ease to developers, but on the other hand, this can lead to security issues because the packages are not signed.
Con Less packages than npm due to a smaller ecosystem
- Bower: 36,000 packages
- Npm: 161,876 total packages (of course, many work only on the server)
As of May 2017 Bower has been deprecated and will not receive any updates with new features. Bugs will still be fixed though for existing projects that use Bower.