yarn why

Show information about why a package is installed.

yarn why <query>

This command will identify why a package has been installed, detailing which other packages depend upon it, for example, or whether it was explicitly marked as a dependency in the package.json manifest.

yarn why jest

yarn why vx.x.x
[1/4] ????  Why do we have the module "jest"...?
[2/4] ????  Initialising dependency graph...
[3/4] ????  Finding dependency...
[4/4] ????  Calculating file sizes...
info Has been hoisted to "jest"
info This module exists because it's specified in "devDependencies".
info Disk size without dependencies: "1.29kB"
info Disk size with unique dependencies: "101.31kB"
info Disk size with transitive dependencies: "20.35MB"
info Amount of shared dependencies: 125

Query argument

The mandatory query argument for yarn why can be any of:

• a package name (as in the above example)
• a package folder; eg: yarn why node_modules/once
• a file within a package folder; eg: yarn why node_modules/once/once.js

The file locations can also be absolute.