package-json-redirects

package-json-redirects

Mode of operation

This strategy is similar to extensionless, but uses directories with package.json stubs that redirect to another file via main (and types) instead of requiring that the implementation (and types) files actually be at the file-system-apparent location.

import "package-json-redirects/one";

An exports-supporting resolver will look up "./one" in the package.json exports, which in turn points either to ./cjs/one.js or ./esm/one.js, depending on the conditions presented by the resolver. A non-exports-supporting resolver will instead find ./one/package.json:

{
  "main": "../cjs/one.js",
  "types": "../types/one.d.ts"
}

And reroute accordingly. The package.json stub chooses to route the non-exports-supporting resolver to the CommonJS files, since Node 11 does not support ESM-format files.

Note that the separate handling of ESM and CJS, as well as the decision to present a unified set of types for the two, is orthogonal to the subpath exports demonstration. (Including separate types for CJS and ESM files, as extensionless does, is often a better choice, and is compatible with this strategy.)

Considerations

Pros:

• Well-supported
• Supports putting implementation and types files in subfolders
• Can model subpaths that map to a file with a different name than the subpath

Cons:

• Lots of files and folders (aesthetic)
• Need to add more every time a new subpath is added
• Cannot support * wildcards; need to create a package.json for all possible matches