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Read the Readme​

Start by reading Vulcan NPM Readme for basic install information.

Then, the package.json list the typical commands you'd expect from an NPM library: build, test...

When adding feature to Vulcan or fixing bug, you'll want to run your code to test it.

  • For components, you can run Storybook: yarn run storybook. Stories let you render components in a certain state, and even automate some operations on them using the "play" function. Documentation:
  • For code, you can run unit tests with Jest: yarn run test or yarn run test <your-test-file-name>.
  • For graphql operations, check test/integration folder: you can run a full Vulcan backend, similar to the backend running in Vulcan Next. You can even use an in-memory Mongo database.

Starter apps with UI like Vulcan Next may have their own specific Storybook and Jest setup. Run cd starters/next to move to the relevant folders.

Advanced: plug to another application​

Using your local Vulcan NPM install within another local application, usually based on Vulcan Next, requires "linking". Linking means that instead of using the package from NPM, you'll tell your application to use the local version of the package. Linking is quite complex (see so we use Yalc to simplify it as much as possible.

To sum it up:

  • In Vulcan NPM, yarn run build && yarn run publish:local will publish all packages in the local Yalc registry
  • In your application, yalc link @vulcanjs/graphql will get the package from this local registry. The command yarn run link:vulcan will do this for all @vulcanjs packages
  • When you update code in Vulcan NPM, rerun yarn run build && yarn run publish:local. Your app will automatically reload with the new version.

A similar documentation exists in Vulcan Next project.

/!\ Next 12 is known to have issues with Yalc + ESM @see

Yarn.lock for the starter apps​

You cannot have a "yarn.lock" in Yarn workspaces, otherwise they are considered as "isolated" and you cannot benefit from Yarn anymore, it won't hoist your packages at the root.

Yet, you might want to generate a yarn.lock for starters app at publication time.

We solve that using this plugin: []

  • Install via yarn plugin import
  • Run yarn
  • Copy the generated yarn.remix.lock in relevant folders
  • In your CI, rename them to yarn.lock. In Remix you can do that during the init step for instance. In Next you might require user to do this manually, or at server startup in a script.

Common issues​

No index.d.ts in dist​

You may end up with a build folder like this:


instead of just having your package code.

You mistakenly imported local code from another package, like importing from ../graphql instead of @vulcanjs/graphql in @vulcanjs/mongo. Find the culprit import and fix them will repair the build.

If your import are correct and you still have this issue, this also seems to unexpectedly affect "@vulcanjs/mongo/client" (client entrypoint) as well. In this case, set a false webpack alias for the faulty package (see react-hooks for instance)

Package self-referencing or leaking server code​

If build:types refuses to overwrite a file, you might have wrongly imported "dist" in your code ; have a package that references itself ; or leak some server code in a shared package.

Forgetting to include tests and stories in tsconfig.json​

This is necessary to get the right typings in VS code. If you ever need to exclude them, eg to fasten the build, then create a dedicated for instance and live tsconfig.json alone.

See this long standing VS code ticket/

If you want to specifiy the files to include in the build, look at instead. This is the file that will actually be used by ts-loader.

TypeScript syntax not recknognized in end-application​

You are importing non built code directly. Example:

error - /code/vulcan-npm/packages/next-material-ui/components/Link.tsx 10:5
Module parse failed: Unexpected token (10:5)
You may need an appropriate loader to handle this file type, currently no loaders are configured to process this file. See
| import MuiLink, { LinkProps as MuiLinkProps } from "@material-ui/core/Link";
> type LinkProps = NextLinkProps &
| MuiLinkProps & {
| activeClassName?: string;

You either forgot to call yarn build or did a direct import (import foobar from "@vulcanjs/reac-hooks/some-not-built-file").

Code not updating during test​

Don't forget to build the code. If you write a test for package "React Hooks", and discover and fix a bug in package "GraphQL", you'll need to rebuild the "GraphQL" package to get the freshest version.

Weird behaviour when linking with React, Apollo, Mongoose.​

Define Peer Dependencies correctly. Many packages have side effects that are problematic if you duplicate them. Those packages should be peer-dependencies in the relevant package.json. You may add them at the root of the project too in development.

Also, use Yalc to install local version of Vulcan NPM within another local app, see the README for more information.

#####Β Example with Mongoose

Make it a peer dependency​

In packages/mongo/package.json:

peerDependencies: {
mongoose: "> 5"

The end application will have only 1 version of Mongoose thanks to this. In ./package.json:

devDependencies: {
"mongoose": "^5.10.16"