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JSPM 2 Resolver

This implements the jspm_packages/[registry]/[name]@[version]/ module resolution lookup while checking the rules defined in package.json and json.json for jspm.

For the full detailed specification of jspm resolution, see the jspm 2.0 resolver specification.

The resolver is fully backwards-compatible with the Node.js --experimental-modules resolver, which in turn is fully-backwards compatible with the traditional CommonJS resolver.


Install with:

npm install @jspm/resolve

Then basic usage is:

import jspmResolve from '@jspm/resolve';

const { resolved, format } = await jspmResolve('specifier', '/path/to/parent/module.js');

The jspm resolver works on file paths that are /-separated. It will still correctly handle the URL normalization rules of the ES Module resolver though, but works on file paths for convenience and performance.

Format, like the Node.js --experimental-modules resolver, is one of commonjs, module, json, builtin, addon or unknown for asset files.



A cache object can be passed to the resolution function that will maintain all the lookup state for fast resolution:

const cache = {};
jspmResolve(name, parent, { cache });


A custom environment can be provided to jspmResolve, representing the conditional paths to take in the resolver.

The default environment is the Node.js development environment:

  browser: false,
  node: true,
  production: false,
  dev: true,
  'react-native': false,
  electron: false,
  deno: false,
  default: true

So a browser production resolution can be made with eg:

jspmResolve(name, parent, {
  env: {
    browser: true,
    production: true

The browser main and map will then be respected, as well as any custom production mappings.

CommonJS Resolve

By default the jspm resolver assumes resolution is coming from an ES module context.

CommonJS modules in Node.js always load all dependencies as CommonJS and this can also be supported in the jspm resolve options by passing the cjsResolve: true option.

This then implements automatic file extension searching as well as always loading the CommonJS format if not an addon or json path.

Synchronous Resolution

jspmResolve.sync can be used to perform synchronous resolution, with an otherwise identical API.


A loader.mjs file is provided which supports the Node.js --experimental-modules loader API:

node --experimental-modules --loader @jspm/resolve/loader.mjs x.js

This applies the jspm resolution to Node.js.


Apache 2.0

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