A "deep import" is simply an ESM import that goes deeper than the package root:
import thingA from 'my-package-name/src/components/thingA'
import thingB from '@my-namespace/my-package-name/src/components/thingA'A namespaced package does not necessitate a deep import if the package name (package.json:name key) contains a slash:
import thingA from '@my-namespace/my-package-name'Relative imports (./path/to/module) are also not considered deep imports, in fact it might be considered bad practice to "shallow import" an exported module from one's own package by it's package.json:main key location (i.e. src/index.js) as this can often cause circular dependencies.
Package bundlers are often used to transpile and condense a project to a distributive, single-file version (i.e. dist/bundle.js). Other packages that try to deep import from such packages experience errors, as the directory structure from src may often not be maintained or even included in the published package.
A developer might deep import a module from a package when it was not intended to be used outside of the scope of that package. Your changing of the name of an internally-used export or your package's directory structure should not require a major version (breaking change) update for a module that was only intended to be consumed internally.
Modules meant to be imported-from by another package should be exported from the package's entry file (i.e. src/index.js) and deep imports should not be used unless otherwise prescribed by the package developer.
Great resource!