fusion-cli/build/jest/resolver.js

// @noflow

/* eslint-env node */

const fs = require('fs');
const {ResolverFactory} = require('enhanced-resolve');

const nodeResolver = ResolverFactory.createResolver({
  fileSystem: fs,
  useSyncFileSystemCalls: true,
  mainFields: ['main'],
  aliasFields: ['es2015', 'es2017'],
});

const browserResolver = ResolverFactory.createResolver({
  fileSystem: fs,
  useSyncFileSystemCalls: true,
  mainFields: ['main'],
  aliasFields: ['browser', 'es2015', 'es2017'],
});

module.exports = function enhancedResolve(modulePath, opts) {
  try {
    if (opts.browser === true) {
      let browserResult = browserResolver.resolveSync(
        {},
        opts.basedir,
        modulePath
      );
      if (browserResult !== false) {
        return browserResult;
      }
      // Fallback to non-browser field if enhanced-resolve produces `false`.
      // Some packages (e.g. object-inspect) use falsy browser field values to
      // indicate that no browser version exists.
      // This isn't handled by enhanced-resolve.
      // So we simply fall back to resolution without browser field in this case
    }

    return nodeResolver.resolveSync({}, opts.basedir, modulePath);
  } catch (err) {
    // Upon failure to resolve, enhanced-resolve throws with a different
    // error message than native Node and no error.code property.
    // This breaks the heuristics of the "bindings" npm library used to
    // locate native code by successively attempting to require potential paths

    // Jest uses the resolver for overloading the native resolution used by
    // the "bindings" libary.

    // So we need to add an error code that "bindings" will recognize,
    // otherwise it will just stop at the first path instead of trying
    // all the possible paths
    // https://github.com/TooTallNate/node-bindings/blob/c8033dcfc04c34397384e23f7399a30e6c13830d/bindings.js#L119
    err.code = 'MODULE_NOT_FOUND';
    throw err;
  }
};