module: reduce ESM ModuleJob memory

Share the empty dependency arrays retained by leaf ModuleJobs instead of allocating separate arrays for each job. Remove unused per-job fields and avoid retaining a default import attributes object when it is not provided.

Assisted-by: OpenCode
Signed-off-by: Uzini <43294422+Uziniii@users.noreply.github.com>

Author: Uziniii

lib/internal/modules/esm/module_job.js

@@ -10,6 +10,7 @@ const {
   ArrayPrototypeSort,
   FunctionPrototype,
   ObjectAssign,
+  ObjectFreeze,
   ObjectSetPrototypeOf,
   PromisePrototypeThen,
   PromiseResolve,
@@ -61,6 +62,9 @@ const {
 } = require('internal/modules/helpers');
 const { getOptionValue } = require('internal/options');
 const noop = FunctionPrototype;
+// Module jobs retain both `linked` and `commonJsDeps`. Share their empty value
+// so leaf modules do not each retain two arrays.
+const kEmptyModuleDependencies = ObjectFreeze([]);
 const {
   ERR_REQUIRE_ASYNC_MODULE,
   ERR_REQUIRE_ESM_RACE_CONDITION,
@@ -296,9 +300,7 @@ class ModuleJobBase {
   constructor(loader, url, importAttributes, phase, isMain, inspectBrk) {
     assert(typeof phase === 'number');
     this.loader = loader;
-    this.importAttributes = importAttributes;
     this.phase = phase;
-    this.isMain = isMain;
     this.inspectBrk = inspectBrk;
 
     this.url = url;
@@ -317,9 +319,12 @@ class ModuleJobBase {
     this.loader.loadCache.set(this.url, this.type, this);
     const moduleRequests = this.module.getModuleRequests();
     // Modules should be aligned with the moduleRequests array in order.
-    const modules = Array(moduleRequests.length);
-    const evaluationDepJobs = [];
-    this.commonJsDeps = Array(moduleRequests.length);
+    const modules = moduleRequests.length === 0 ?
+      kEmptyModuleDependencies : Array(moduleRequests.length);
+    const evaluationDepJobs = moduleRequests.length === 0 ?
+      kEmptyModuleDependencies : [];
+    this.commonJsDeps = moduleRequests.length === 0 ?
+      kEmptyModuleDependencies : Array(moduleRequests.length);
     try {
       for (let idx = 0; idx < moduleRequests.length; idx++) {
         const request = moduleRequests[idx];
@@ -402,7 +407,7 @@ class ModuleJob extends ModuleJobBase {
    *   first line paused in the debugger (because --inspect-brk is passed).
    * @param {ModuleRequestType} requestType Type of the module request.
    */
-  constructor(loader, url, importAttributes = { __proto__: null }, moduleOrModulePromise,
+  constructor(loader, url, importAttributes, moduleOrModulePromise,
               phase = kEvaluationPhase, isMain, inspectBrk, requestType) {
     super(loader, url, importAttributes, phase, isMain, inspectBrk);
 
@@ -452,9 +457,12 @@ class ModuleJob extends ModuleJobBase {
     // Create an ArrayLike to avoid calling into userspace with `.then`
     // when returned from the async function.
     // Modules should be aligned with the moduleRequests array in order.
-    const modulePromises = Array(moduleRequests.length);
-    const evaluationDepJobs = [];
-    this.commonJsDeps = Array(moduleRequests.length);
+    const modulePromises = moduleRequests.length === 0 ?
+      kEmptyModuleDependencies : Array(moduleRequests.length);
+    const evaluationDepJobs = moduleRequests.length === 0 ?
+      kEmptyModuleDependencies : [];
+    this.commonJsDeps = moduleRequests.length === 0 ?
+      kEmptyModuleDependencies : Array(moduleRequests.length);
     for (let idx = 0; idx < moduleRequests.length; idx++) {
       const request = moduleRequests[idx];
       // Explicitly keeping track of dependency jobs is needed in order