@@ -47,6 +47,11 @@ interface LibraryReference {
4747 readonly shortName : string ;
4848}
4949
50+ type Export = string | {
51+ readonly import ?: string ;
52+ readonly require ?: string ;
53+ } ;
54+
5055interface PackageJson {
5156 readonly main ?: string ;
5257 readonly description ?: string ;
@@ -103,7 +108,7 @@ interface PackageJson {
103108 */
104109 readonly exports ?: Record < string , string > ;
105110 } ;
106- exports ?: Record < string , string > ;
111+ exports ?: Record < string , Export > ;
107112}
108113
109114/**
@@ -269,7 +274,10 @@ async function prepareSourceFiles(libraries: readonly LibraryReference[], packag
269274 // Control 'exports' field of the 'package.json'. This will control what kind of 'import' statements are
270275 // allowed for this package: we only want to allow the exact import statements that we want to support.
271276 packageJson . exports = {
272- '.' : './index.js' ,
277+ '.' : {
278+ import : './index.js' ,
279+ require : './lazy-index.js' ,
280+ } ,
273281
274282 // We need to expose 'package.json' and '.jsii' because 'jsii' and 'jsii-reflect' load them using
275283 // require(). (-_-). Can be removed after https://github.com/aws/jsii/pull/3205 gets merged.
@@ -281,12 +289,15 @@ async function prepareSourceFiles(libraries: readonly LibraryReference[], packag
281289 } ;
282290
283291 // We use the index.ts to compile type definitions.
284- // At the very end we replace the compiled index.js file with our fixed version exports.js.
285- // exports.js has the top level submodules exports defined as a getter function,
286- // so they are not automatically loaded when importing from `aws-cdk-lib`.
292+ //
293+ // We build two indexes: one for eager loading (used by ESM modules), and one
294+ // for lazy loading (used by CJS modules). The lazy loading will result in faster
295+ // loading times, because we don't have to load and parse all submodules right away,
296+ // but is not compatible with ESM's loading algorithm.
297+ //
287298 // This improves AWS CDK app performance by ~400ms.
288299 const indexStatements = new Array < string > ( ) ;
289- const exportsStatements = new Array < string > ( ) ;
300+ const lazyExports = new Array < string > ( ) ;
290301
291302 for ( const library of libraries ) {
292303 const libDir = path . join ( libRoot , library . shortName ) ;
@@ -297,19 +308,21 @@ async function prepareSourceFiles(libraries: readonly LibraryReference[], packag
297308 }
298309 if ( library . shortName === 'core' ) {
299310 indexStatements . push ( `export * from './${ library . shortName } ) ;
300- exportsStatements . unshift ( `export * from './${ library . shortName } ) ;
311+ lazyExports . unshift ( `export * from './${ library . shortName } ) ;
301312 } else {
302- indexStatements . push ( `export * as ${ library . shortName . replace ( / - / g, '_' ) } ${ library . shortName } ) ;
303- exportsStatements . push ( `Object.defineProperty(exports, '${ library . shortName . replace ( / - / g, '_' ) } ${ library . shortName } ) ;
313+ const exportName = library . shortName . replace ( / - / g, '_' ) ;
314+
315+ indexStatements . push ( `export * as ${ exportName } ${ library . shortName } ) ;
316+ lazyExports . push ( `Object.defineProperty(exports, '${ exportName } ${ library . shortName } ) ;
304317 }
305318 copySubmoduleExports ( packageJson . exports , library , library . shortName ) ;
306319 }
307320
308321 // make the exports.ts file pass linting
309- exportsStatements . unshift ( '/* eslint-disable @typescript-eslint/no-require-imports */' ) ;
322+ lazyExports . unshift ( '/* eslint-disable @typescript-eslint/no-require-imports */' ) ;
310323
311324 await fs . writeFile ( path . join ( libRoot , 'index.ts' ) , indexStatements . join ( '\n' ) , { encoding : 'utf8' } ) ;
312- await fs . writeFile ( path . join ( libRoot , 'exports .ts' ) , exportsStatements . join ( '\n' ) , { encoding : 'utf8' } ) ;
325+ await fs . writeFile ( path . join ( libRoot , 'lazy-index .ts' ) , lazyExports . join ( '\n' ) , { encoding : 'utf8' } ) ;
313326
314327 console . log ( '\t🍺 Success!' ) ;
315328}
@@ -320,13 +333,21 @@ async function prepareSourceFiles(libraries: readonly LibraryReference[], packag
320333 * Replace the original 'main' export with an export of the new '<submodule>/index.ts` file we've written
321334 * in 'transformPackage'.
322335 */
323- function copySubmoduleExports ( targetExports : Record < string , string > , library : LibraryReference , subdirectory : string ) {
336+ function copySubmoduleExports ( targetExports : Record < string , Export > , library : LibraryReference , subdirectory : string ) {
324337 const visibleName = library . shortName ;
325338
326339 // Do both REAL "exports" section, as well as virtual, ubergen-only "exports" section
327340 for ( const exportSet of [ library . packageJson . exports , library . packageJson . ubergen ?. exports ] ) {
328341 for ( const [ relPath , relSource ] of Object . entries ( exportSet ?? { } ) ) {
329- targetExports [ `./${ unixPath ( path . join ( visibleName , relPath ) ) } ] = `./${ unixPath ( path . join ( subdirectory , relSource ) ) } ;
342+ targetExports [ `./${ unixPath ( path . join ( visibleName , relPath ) ) } ] = resolveExport ( relSource ) ;
343+ }
344+ }
345+
346+ function resolveExport < A extends Export > ( exp : A ) : A {
347+ if ( typeof exp === 'string' ) {
348+ return `./${ unixPath ( path . join ( subdirectory , exp ) ) } as any ;
349+ } else {
350+ return Object . fromEntries ( Object . entries ( exp ) . map ( ( [ k , v ] ) => [ k , v ? resolveExport ( v ) : undefined ] ) ) as any ;
330351 }
331352 }
332353
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