❓ package.json

The targets object in package.json

ΒΆ Fields

These are the fields that Parcel uses for its configuration:

ΒΆ main / module / browser

These are common fields used by other tools as well,

package.json:
{
"main": "dist/main/index.js",
"module": "dist/module/index.js",
"browser": "dist/browser/index.js"
}

They default to library mode (meaning they don't bundle dependencies): (see also targets)

If one these fields is specified, Parcel will create a target for that field (no property in targets is needed)

To make Parcel ignore one of these fields, specify false in target.(main|browser|module):

package.json:
{
"main": "unrelated.js",
"targets": {
"main": false
}
}

If the browser field is an object, package.json#browser[pkgName] can be used instead of package.json#browser.

ΒΆ custom targets

To create your own target (without any of the semantics of the common target described previously), add a top-level field with your target's name and output path. You also need to add it to targets to make Parcel recognize that field.

package.json:
{
"app": "www/index.js",
"targets": {
"app": {}
}
}

ΒΆ source

Specify the entry points for your source code which gets mapped to your targets, can be a string or an array.

package.json:
{
"source": "src/index.js"
}
package.json:
{
"source": ["src/index.js", "src/index.html"]
}

See Specifying Entrypoints.

ΒΆ targets

Targets are configured via the package.json#targets field.

{
"app": "dist/browser/index.js",
"appModern": "dist/browserModern/index.js",
"targets": {
"app": {
"engines": {
"browsers": "> 0.25%"
}
},
"appModern": {
"engines": {
"browsers": "Chrome 70"
}
}
}
}

Each target has a name which corresponds to a top-level package.json field such as package.json#main or package.json#app which specify the primary entry point for that target.

Each of those targets contains the target's environment configuration (all of these properties are optional):

Option Possible values Description
context see below In which runtime the bundles should run.
distDir string Specify output folder (as opposed to output file)
engines package.json#engines Higher priority than package.json#engines
includeNodeModules see below Whether to bundle all/none/some node_module dependencies
isLibrary boolean Library as in "npm library"
minify boolean Whether to enable minification (exact behaviour is determined by plugins).
Set by --no-minify
outputFormat 'global' | 'esmodule' | 'commonjs' Which type of imports/exports should be emitted
publicUrl string The public url of the bundle at runtime
scopeHoist boolean Whether to enable scope hoisting
Needs to be true for ESM and CommonJS outputFormat.
Set by --no-scope-hoist
sourceMap see below Enable/disable sourcemap and set options.
Overwritten by --no-source-maps

However, a lot of the normal configuration for building a library is already provided by default for you:

targets = {
main: {
engines: {
node: value("package.json#engines.node"),
browsers: unless exists("package.json#browser") then value("package.json#browserlist")
},
isLibrary: true
},
module: {
engines: {
node: value("package.json#engines.node"),
browsers: unless exists("package.json#browser") then value("package.json#browserlist")
},
isLibrary: true
},
browser: {
engines: {
browsers: value("package.json#browserslist")
},
isLibrary: true
},
...value("package.json#targets"),
}
ΒΆ context

Possible values are 'node' | 'browser' | 'web-worker' | 'service-worker' | 'electron-main' | 'electron-renderer'.

These values can be used by plugins (e.g. a service worker url should not contain a hash, a webworker can use importScripts).

For the common targets, these are inferred from the target:

ΒΆ includeNodeModules

This fields defaults to false when isLibrary is true. Possible values are:

See Module Resolution for more information.

ΒΆ sourceMap

Can be a boolean (to simply enable / disable source maps) or an option (which is somewhat equivlant to true):

Option Default value Description
inline false Include the sourcemap as a data-url in the bundle (in the sourceMappingURL)
inlineSources false Should the sourcemap contain the sources contents (otherwise, they will be loaded from ${sourceRoot}/$(name))
sourceRoot path.relative(bundle, pojectRoot) Essentially the public url for the sources

The --no-source-maps CLI parameter sets the default value to false (as opposed to true).

ΒΆ engines / browserslist

These top-level fields set the default value for target.*.engines.browsers and target.*.engines, respectively.

Specifies the environment.

package.json:
{
"browserslist": ["> 0.2%", "not dead"]
}
package.json:
{
"engines": {
"node": ">=4.x",
"electron": ">=2.x",
"browsers": "> 0.25%"
}
}

ΒΆ alias

See Module Resolution

ΒΆ Which package.json is used when specifying multiple entries (packages)

All paths are relative to /some/dir/my-monorepo.

cwd entries used pkg.json#* (fields described below)
.. packages/*/src/**/*.js package.json
. packages/*/src/**/*.js package.json
packages/ packages/*/src/**/*.js package.json
packages/pkg-a packages/pkg-a/src/index.js packages/pkg-a/package.json
packages/pkg-a/src packages/pkg-a/src/index.js packages/pkg-a/package.json