When comparing JSPM vs Bower, the Slant community recommends JSPM for most people. In the question“What are the best open source front-end package managers?” JSPM is ranked 4th while Bower is ranked 5th. The most important reason people chose JSPM is:
JSPM is registry agnostic, it can pull packages from npm and github and is built in such a way it can support more.
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Pros
Pro Registry agnostic
JSPM is registry agnostic, it can pull packages from npm and github and is built in such a way it can support more.
Pro Module style agnostic
Loads ES6, AMD, CommonJS and globals.
Pro Can transcompile ES6, JSX and Typescript
Pro Much faster than Webpack or Browserify
While Webpack and Browserify recompile the source code using Babel, jspm is the only packager that can load prebuild/minified code downloaded from the npm registry.
Pro Bundled based on imported modules without any config
Create the bundle file without config and add only the modules imported.
Pro Switch between async or sync load
With a simple command you could change between load the modules async by systemjs or sync with a bundle file.
Pro Easy install packages from npm, github or any git repository
Pro Versioned package urls
It creates a packages folders which are versioned. This makes it future proof for a time where we stop bundling all the code. In the following presentation Guy Bedford calls bundling an anti-pattern.
Pro Very easy to start with
Pro Manages non-JavaScript components
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 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 Largest front-end specific package registry
Although npm is the largest javascript package manager, Bower is the most popular one built specifically for the front-end. With over 16000 components in its registry, pretty much every component you can think of is supported.
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 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.
Cons
Con You need to be an expert to write shims
You can load any module. But that comes with the price:
you need to find or write configs to load a particular rare module.
Con Doesn't hide complexity
JSPM doesn't try to hide complexity from the user. I.e. when some issue emerges you need understand a lot to be able to patch it or create a workaround.
Con Watcher has bugs
Watching would benefit from improvements
Con Unstable API
0.17 is still in beta. 0.16 is lacking features.
Con Poor bundler performance
Bundling performance is slow, though offset by the fact that bundling is not required during development, since it can load dependencies asynchronously.
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 Deprecated
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.
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 Difficult to create bundles
To create a minified bundle of all the required JS dependencies other tools need to be used.
For example a JavaScript task runner which will automatically concatenate JavaScript files and minify them will be needed. Although it's done automatically, it's still extra work because the task runner needs to be configured.
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)