package.json
The manifest file of a package. It contains all the package's metadata, including dependencies, title, author, et cetera. This is a standard preserved across all major Node.JS package managers, including pnpm.
engines
You can specify the version of Node and pnpm that your software works on:
{
"engines": {
"node": ">=10",
"pnpm": ">=3"
}
}
During local development, pnpm will always fail with an error message
if its version does not match the one specified in the engines
field.
Unless the user has set the engine-strict
config flag (see .npmrc), this
field is advisory only and will only produce warnings when your package is
installed as a dependency.
dependenciesMeta
Additional meta information used for dependencies declared inside dependencies
, optionalDependencies
, and devDependencies
.
dependenciesMeta.*.injected
If this is set to true
for a dependency that is a local workspace package, that package will be installed by creating a hard linked copy in the virtual store (node_modules/.pnpm
).
If this is set to false
or not set, then the dependency will instead be installed by creating a node_modules
symlink that points to the package's source directory in the workspace. This is the default, as it is faster and ensures that any modifications to the dependency will be immediately visible to its consumers.
For example, suppose the following package.json
is a local workspace package:
{
"name": "card",
"dependencies": {
"button": "workspace:1.0.0"
}
}
The button
dependency will normally be installed by creating a symlink in the node_modules
directory of card
, pointing to the development directory for button
.
But what if button
specifies react
in its peerDependencies
? If all projects in the monorepo use the same version of react
, then there is no problem. But what if button
is required by card
that uses react@16
and form
that uses react@17
? Normally you'd have to choose a single version of react
and specify it using devDependencies
of button
. Symlinking does not provide a way for the react
peer dependency to be satisfied differently by different consumers such as card
and form
.
The injected
field solves this problem by installing a hard linked copies of button
in the virtual store. To accomplish this, the package.json
of card
could be configured as follows:
{
"name": "card",
"dependencies": {
"button": "workspace:1.0.0",
"react": "16"
},
"dependenciesMeta": {
"button": {
"injected": true
}
}
}
Whereas the package.json
of form
could be configured as follows:
{
"name": "form",
"dependencies": {
"button": "workspace:1.0.0",
"react": "17"
},
"dependenciesMeta": {
"button": {
"injected": true
}
}
}
With these changes, we say that button
is an "injected dependency" of card
and form
. When button
imports react
, it will resolve to react@16
in the context of card
, but resolve to react@17
in the context of form
.
Because injected dependencies produce copies of their workspace source directory, these copies must be updated somehow whenever the code is modified; otherwise, the new state will not be reflected for consumers. When building multiple projects with a command such as pnpm --recursive run build
, this update must occur after each injected package is rebuilt but before its consumers are rebuilt. For simple use cases, it can be accomplished by invoking pnpm install
again, perhaps using a package.json
lifecycle script such as "prepare": "pnpm run build"
to rebuild that one project. Third party tools such as pnpm-sync and pnpm-sync-dependencies-meta-injected provide a more robust and efficient solution for updating injected dependencies, as well as watch mode support.
peerDependenciesMeta
This field lists some extra information related to the dependencies listed in
the peerDependencies
field.
peerDependenciesMeta.*.optional
If this is set to true, the selected peer dependency will be marked as optional by the package manager. Therefore, the consumer omitting it will no longer be reported as an error.
For example:
{
"peerDependencies": {
"foo": "1"
},
"peerDependenciesMeta": {
"foo": {
"optional": true
},
"bar": {
"optional": true
}
}
}
Note that even though bar
was not specified in peerDependencies
, it is
marked as optional. pnpm will therefore assume that any version of bar is fine.
However, foo
is optional, but only to the required version specification.
publishConfig
It is possible to override some fields in the manifest before the package is packed. The following fields may be overridden:
To override a field, add the publish version of the field to publishConfig
.
For instance, the following package.json
:
{
"name": "foo",
"version": "1.0.0",
"main": "src/index.ts",
"publishConfig": {
"main": "lib/index.js",
"typings": "lib/index.d.ts"
}
}