When comparing JSPM vs Jam, the Slant community recommends JSPM for most people. In the question“What are the best front-end package managers?” JSPM is ranked 3rd while Jam 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 Has a central package repository
A central repository provides more guarantees about the availability of the package. With requiring directly from repository urls, the entire project could potentially be taken down on a whim.
Pro Community is focused on client side javascript
Because Jam only manages Javascript and only works on the client side, you have the assurance that any packages listed are AMD compatible for asynchronous loading.
Pro Architecture independent
Jam's only a front-end package manager, the rest of your server can be on a different architecture or framework. No matter what the architecture, Jam will integrate easily with it.
Pro Provides the best AMD compatibility allowing for better asynchronous loading
Jam requires AMD (Asynchronous Module Definition), which means faster package loading, as it can be done asynchronously.
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 Forced AMD compatibility means fewer libraries
AMD is currently not as popular as CommonJS modules, which means if a library isn't supported, you'll have to deal with it yourself.