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Eik is for serving ESM and CSS but we use the term packages when we refer what is uploaded to an Eik server. A package can contain any set of files which are considered to be static assets on a web site. Despite being agnostic in its opinion about what a package can contain, Eik does have a package type definition which comes into play when organizing assets.

Package Types

Eik differentiates between the types of packages it hosts. These are: Packages, NPM Packages and Import Maps. On the server, these different types live under separate URL namespaces to avoid conflicts with each other.

Eik Packages

Eik packages are normally produced by websites and web applications. Such a package typically consists of bundled application code which, most of the time, does not really make much sense to publish as a module to a public repository such as NPM.

Packages live under the /pkg/ namespace on an Eik server.

NPM Packages

NPM packages are modules replicated from the NPM repository with the intention that they be loadable by browsers. This is similar to what unpkg and pika do, with the exception that Eik does not proxy NPM modules as Unpkg and Pika do. Eik has taken a different approach and it is necessary to manually publish modules from NPM to Eik as well as do any transpiling from (for example) CommonJS to ESM as a manual process before publishing.

NPM Packages live under the /npm/ namespace on an Eik server.

Import Maps

Import Maps are handled as single JSON files in Eik and not treated as a package. It's only possible to upload a single file and not a group of files like it is when uploading packages.

Import Maps live under the /map/ namespace on a Eik server.

Naming and versioning

A package intended to be published to an Eik server should follow the NPM module naming convention:

  • package name length should be greater than zero
  • all characters in a package name must be lowercase i.e., no uppercase or mixed case names are allowed
  • package name can consist of hyphens
  • package name must not contain non-url-safe characters (since name ends up being part of a URL)
  • package name should not start with . or _
  • package name should not contain leading or trailing spaces
  • package name should not contain any of the following characters: ~)('!*
  • package name cannot be the same as a node.js/io.js core module nor a reserved/blacklisted name. For example, the following names are invalid:
    • http
    • stream
    • node_modules
    • favicon.ico
  • package name length cannot exceed 214

All packages published to an Eik server is immutable and versioned with Semantic Versioning. This makes it possible to differentiate between what are considered smaller changes to a package which should not break behaviour in a dependency from changes which can be breaking.

Since packages are immutable, the Eik server will set an infinite HTTP cache control header on all files belonging to a package to make use of browser caching.


Aliasing can be applied to all packages and is a way of having a static URL reference, which can change, to a version of a package. Aliases are mutable and can be set to point to different versions of a package. The alias URL will do a redirect to the full version that it is set to point to.

Lets say we publish lit-html version 1.1.1 as an NPM package to an Eik server. It will then live on the following URL:

If we then create an alias for this version it will live on the following URL:

Any request to any file under this alias will be redirected to the same path under the package version it refers too.

A request to the following file under the alias:

will redirect to:

Aliasing is not automatic in Eik. Aliases must be created or updated manually when a version of a package is published to an Eik server.

Aliasing and versioning

Aliasing is tied to the semantic version of each package where the alias is the major version as a single digit pointing to a given full version of the same major version. That means that all 1.x versions of a package can have a v1 alias and all 2.x versions of the same package can have a v2 alias at the same time.

This is a feature to make sure there is a way to publish breaking changes in a package without breaking its dependencies. In semantic versioning patch and minor versions are supposed to not contain breaking changes while a major version can contain breaking changes so in a situation where a package introduces a breaking change it should, according to semantic versioning, be published as a new major version.

This breaks a bit with what Eik is trying to solve if we look at the challenge we outlined in our introduction but the handling of breaking changes is probably the one place where it's acceptable not to align all dependencies of a package to the same version of it.