Offline mode

[gaearon]

npm wizards, we need your help!

Per @pselle’s suggestion, we should try to find a way to make create-react-app work offline.

I’m not well versed in npm flags and likely won’t have time for this, so this is a perfect opportunity for you to contribute and significantly improve the user experience of Create React App.

Here is the behavior we’re looking for:

• Existing requirement: create-react-app my-app should use the most recent version of react-scripts if you are online. We are not changing this: we always want the users to get the most recent one.
• New requirement: create-react-app my-app should not crash offline if you ran it at least once before. It should be able to use locally cached react-scripts in this case, if it exists.
• Bonus: create-react-app my-app should use cached react-scripts if it knows the latest npm version is cached locally. In other words, even if you are online, we shouldn’t just refetch the whole thing if we have it locally and we know it is the latest version. This is not required but would make a big difference for most people.
• Acceptable tradeoff: we are fine with not installing the latest transitive dependencies. In other words it’s fine if react-scripts depends on some-package@1.0.0, then some-package@1.0.1 comes out, but we keep using the cached some-package@1.0.0.

How to achieve this? I have no idea.

Maybe this would be helpful: https://addyosmani.com/blog/using-npm-offline/.

We already use bundledDependencies (which is a bit unusual) as part of our build process so in reality react-scripts is being downloaded as a single tarball rather than through the usual npm process. Perhaps this can give us the leverage to make this better (e.g. by caching that tarball somehow).

[apaleslimghost]

I'm not sure how this fits with bundledDependencies but in npm >= 3.9 --cache-min=999999999 is pretty much exactly what you're looking for https://github.com/npm/npm/releases/tag/v3.9.0

[gaearon]

I’m concerned about issues like this: npm/npm#8581. If the solution involves --cache-min, and --cache-min causes weird crashes in some conditions, we must:

1. Understand why this happens and whether our users will be affected by this
2. Be resistant to such failures (e.g. by retrying npm install without that flag if it fails)

If you know how to handle these points, I’m happy to review a PR explaining your thought process.

[apaleslimghost]

I believe that issue is exactly what 3.9 fixes. You could detect npm version and avoid the flag if running older than 3.9? I'd be happy to do a pr, is this the right call to modify?

[gaearon]

Yes, this is the right call. What you suggest seems reasonable, please go for it!

It would also help if you could help me understand how to reproduce exactly that issue in < 3.9 so we can verify 3.9 indeed fixes it in our case.

[apaleslimghost]

To reproduce you need a package a that depends on b@^1.1.0, where a is not in the cache, and b@1.0.0 is in the cache but b@1.1.0 is not. Then try to install a with ---cache-min=99999999. Instead of downloading the new version of b, npm will only try versions from the cache, and fail because there is no compatible version.

(Hope that helps, it's not a trivial issue...)

[gaearon]

Yeah, I meant this in the context of react-scripts.

If you submitted a PR, I’d appreciate step-by-step instructions to reproduce this exact issue with react-scripts just so I can verify that it was broken before 3.9 but fixed in it.

[apaleslimghost]

Oh, right, sorry. The user would have to have an old version of one of the dependencies of react-scripts in cache but not react-scripts itself. So if they had e.g. babel-core@6.10 in cache and tried to run npm install --cache-min=Infinity react-scripts (which depends on babel-core@6.11) it would hit the issue.

[gaearon]

Thanks for explanation! I’ll try reproing that if you submit a PR. 😉

[apaleslimghost]

Just double checking I'm editing global-cli/index.js? That's a pretty scary warning 😉

[gaearon]

Yea, it’s meant to prevent accidental breaking changes since people almost never have to update the CLI, and since old CLIs must always work with new react-scripts even after breaking changes in react-scripts. Your change is safe tho.

[gafemoyano]

Did anyone get to this issue? Does create-react-app work properly offline?

[gaearon]

No but if you pick up #375 and make it pass Travis, it could be in next version :-)