esm: refactor dynamic modules

This is a change from the ecmascript-modules fork.
There is no change to behavior and we would like to
upstream to reduce the delta between our repos.
Refs: https://github.com/nodejs/ecmascript-modules#9
PR-URL: #24560
Refs: nodejs/ecmascript-modules#9
Reviewed-By: Guy Bedford <guybedford@gmail.com>
Reviewed-By: Gus Caplan <me@gus.host>

Author: MylesBorins

lib/internal/modules/cjs/loader.js

@@ -623,23 +623,24 @@ Module.prototype.load = function(filename) {
 if(experimentalModules){
 if(asyncESM===undefined)lazyLoadESM();
 constESMLoader=asyncESM.ESMLoader;
-consturl=pathToFileURL(filename);
-consturlString=`${url}`;
+consturl=`${pathToFileURL(filename)}`;
+constmodule=ESMLoader.moduleMap.get(url);
+// create module entry at load time to snapshot exports correctly
 constexports=this.exports;
-if(ESMLoader.moduleMap.has(urlString)!==true){
+if(module!==undefined){// called from cjs translator
+module.reflect.onReady((reflect)=>{
+reflect.exports.default.set(exports);
+});
+}else{// preemptively cache
 ESMLoader.moduleMap.set(
-urlString,
+url,
 newModuleJob(ESMLoader,url,async()=>{
-constctx=createDynamicModule(
-['default'],url);
-ctx.reflect.exports.default.set(exports);
-returnctx;
+returncreateDynamicModule(
+['default'],url,(reflect)=>{
+reflect.exports.default.set(exports);
+});
 })
 );
-}else{
-constjob=ESMLoader.moduleMap.get(urlString);
-if(job.reflect)
-job.reflect.exports.default.set(exports);
 }
 }
 };

lib/internal/modules/esm/create_dynamic_module.js

@@ -1,6 +1,6 @@
 'use strict';
 
-const{ ModuleWrap }=internalBinding('module_wrap');
+const{ ModuleWrap, callbackMap}=internalBinding('module_wrap');
 constdebug=require('util').debuglog('esm');
 constArrayJoin=Function.call.bind(Array.prototype.join);
 constArrayMap=Function.call.bind(Array.prototype.map);
@@ -10,50 +10,47 @@ const createDynamicModule = (exports, url = '', evaluate) => {
 `creating ESM facade for ${url} with exports: ${ArrayJoin(exports,', ')}`
 );
 constnames=ArrayMap(exports,(name)=>`${name}`);
-// Create two modules: One whose exports are get- and set-able ('reflective'),
-// and one which re-exports all of these but additionally may
-// run an executor function once everything is set up.
-constsrc=`
- export let executor;
-${ArrayJoin(ArrayMap(names,(name)=>`export let $${name};`),'\n')}
- /* This function is implicitly returned as the module's completion value */
- (() => ({
- setExecutor: fn => executor = fn,
- reflect: {
- exports: { ${
-ArrayJoin(ArrayMap(names,(name)=>`
-${name}: {
- get: () => $${name},
- set: v => $${name} = v
- }`),', \n')}
- }
- }
- }));`;
-constreflectiveModule=newModuleWrap(src,`cjs-facade:${url}`);
-reflectiveModule.instantiate();
-const{ setExecutor, reflect }=reflectiveModule.evaluate(-1,false)();
-// public exposed ESM
-constreexports=`
- import {
- executor,
-${ArrayMap(names,(name)=>`$${name}`)}
- } from "";
- export {
-${ArrayJoin(ArrayMap(names,(name)=>`$${name} as ${name}`),', ')}
- }
- if (typeof executor === "function") {
- // add await to this later if top level await comes along
- executor()
- }`;
-if(typeofevaluate==='function'){
-setExecutor(()=>evaluate(reflect));
-}
-constmodule=newModuleWrap(reexports,`${url}`);
-module.link(async()=>reflectiveModule);
-module.instantiate();
-reflect.namespace=module.namespace();
+
+constsource=`
+${ArrayJoin(ArrayMap(names,(name)=>
+`let $${name};
+export { $${name} as ${name} };
+import.meta.exports.${name} = {
+ get: () => $${name},
+ set: (v) => $${name} = v,
+};`),'\n')
+}
+
+import.meta.done();
+`;
+
+constm=newModuleWrap(source,`${url}`);
+m.link(()=>0);
+m.instantiate();
+
+constreadyfns=newSet();
+constreflect={
+namespace: m.namespace(),
+exports: {},
+onReady: (cb)=>{readyfns.add(cb);},
+};
+
+callbackMap.set(m,{
+initializeImportMeta: (meta,wrap)=>{
+meta.exports=reflect.exports;
+meta.done=()=>{
+evaluate(reflect);
+reflect.onReady=(cb)=>cb(reflect);
+for(constfnofreadyfns){
+readyfns.delete(fn);
+fn(reflect);
+}
+};
+},
+});
+
 return{
- module,
+module: m,
  reflect,
 };
 };

lib/internal/modules/esm/translators.js

@@ -60,9 +60,10 @@ translators.set('cjs', async (url, isMain) => {
 constmodule=CJSModule._cache[
 isWindows ? StringReplace(pathname,winSepRegEx,'\\') : pathname];
 if(module&&module.loaded){
-constctx=createDynamicModule(['default'],url);
-ctx.reflect.exports.default.set(module.exports);
-returnctx;
+constexports=module.exports;
+returncreateDynamicModule(['default'],url,(reflect)=>{
+reflect.exports.default.set(exports);
+});
 }
 returncreateDynamicModule(['default'],url,()=>{
 debug(`Loading CJSModule ${url}`);