lib: add primitive fast path to structuredClone

benchmark/misc/structured-clone.js

@@ -4,14 +4,19 @@ const common = require('../common.js');
 const assert = require('assert');
 
 const bench = common.createBenchmark(main, {
-  type: ['string', 'object', 'arraybuffer'],
+  type: ['primitive', 'string', 'object', 'arraybuffer'],
   n: [1e4],
 });
 
 function main({ n, type }) {
   const data = [];
 
   switch (type) {
+    case 'primitive':
+      for (let i = 0; i < n; ++i) {
+        data.push(i);
+      }
+      break;
     case 'string':
       for (let i = 0; i < n; ++i) {
         data.push(new Date().toISOString());

lib/internal/worker/js_transferable.js

@@ -115,6 +115,17 @@ function structuredClone(value, options) {
     throw new ERR_MISSING_ARGS('The value argument must be specified');
   }
 
+  // Fast path: primitives clone to themselves, so skip the native
+  // serialize/deserialize round-trip when no options were provided.
+  // Symbols are excluded. they are not cloneable and must throw below.
+  if (options === undefined &&
+      (value === null ||
+       (typeof value !== 'object' &&
+        typeof value !== 'function' &&
+        typeof value !== 'symbol'))) {
+    return value;
+  }
+
   const idlOptions = webidl.converters.StructuredSerializeOptions(
     options,
     {

test/parallel/test-structuredClone-global.js

@@ -27,6 +27,17 @@ assert.strictEqual(structuredClone(undefined, null), undefined);
 // Transfer can be null or undefined.
 assert.strictEqual(structuredClone(undefined, { }), undefined);
 
+// Primitives clone to themselves.
+assert.strictEqual(structuredClone(null), null);
+assert.strictEqual(structuredClone(1), 1);
+assert.strictEqual(structuredClone('x'), 'x');
+assert.strictEqual(structuredClone(true), true);
+assert.strictEqual(structuredClone(10n), 10n);
+// -0 is preserved.
+assert.ok(Object.is(structuredClone(-0), -0));
+// Symbols are not cloneable and must throw.
+assert.throws(() => structuredClone(Symbol()), { name: 'DataCloneError' });
+
 // Transferables or its subclasses should be received with its closest transferable superclass
 for (const StreamClass of [ReadableStream, WritableStream, TransformStream]) {
   const original = new StreamClass();