❓ package.json

¶ Fields

These are the fields that Parcel uses for its configuration:

¶ main / module / browser

These are common fields used by other tools as well,

{
  "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)

• main (and module) are the standard entry points to your library, module defaults to ESM module output.
• browser is intended for a browser-specific build (e.g. without some native features).

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):

{
  "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.

Note that there will always be at least one target, even with main: false. (So the default target will be used instead of main.)

¶ 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.

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

¶ source

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

{
  "source": "src/index.js"
}

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

See Specifying Entrypoints.

¶ 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):

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"),
}

¶ 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:

• The main target has the context node if there is browser target or engines.node != null && engines.browsers == null, and browser otherwise.
• The module target has the context node if there is browser target and browser otherwise.
• The browser target has context browser.

¶ includeNodeModules

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

• false: to include none node_modules package
• an array: a list of packages names or wildcards to include
• an object: includeNodeModules[pkgName] ?? true determines if it is included. (e.g. { "lodash": false })

See Module Resolution for more information.

¶ sourceMap

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

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

¶ engines / browserslist

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

Specifies the environment.

{
  "browserslist": ["> 0.2%", "not dead"]
}

{
  "engines": {
    "node": ">=4.x",
    "electron": ">=2.x",
    "browsers": "> 0.25%"
  }
}

¶ alias

See Module Resolution

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

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