lib: optimize TextEncoder.encode for short strings

lib/internal/encoding.js

@@ -13,6 +13,7 @@ const {
   StringPrototypeSlice,
   Symbol,
   SymbolToStringTag,
+  Uint8Array,
 } = primordials;
 
 const { FastBuffer } = require('internal/buffer');
@@ -338,11 +339,26 @@ function getEncodingFromLabel(label) {
 
 let lazyInspect;
 
+const kSmallEncodeLength = 32;
+let smallEncodeScratch;
+
 class TextEncoder {
   #encoding = 'utf-8';
 
   #encode(input) {
-    return encodeUtf8String(`${input}`);
+    input = `${input}`;
+    if (input.length > kSmallEncodeLength) {
+      return encodeUtf8String(input);
+    }
+
+    smallEncodeScratch ??= new Uint8Array(kSmallEncodeLength * 3);
+    encodeInto(input, smallEncodeScratch);
+    const written = encodeIntoResults[1];
+    const result = new Uint8Array(written);
+    for (let i = 0; i < written; i++) {
+      result[i] = smallEncodeScratch[i];
+    }
+    return result;
   }
 
   #encodeInto(input, dest) {

test/parallel/test-whatwg-encoding-custom-textencoder-short.js

@@ -0,0 +1,33 @@
+'use strict';
+
+// Tests TextEncoder.prototype.encode() around the short string path.
+
+require('../common');
+
+const assert = require('assert');
+
+const encoder = new TextEncoder();
+
+const inputs = [
+  '',
+  'a',
+  'a'.repeat(32),
+  'a'.repeat(33),
+  '\xff'.repeat(32),
+  'ğ'.repeat(32),
+  'ࠀ'.repeat(32),
+  '\u{1F44B}'.repeat(16),
+  '\u{1F44B}'.repeat(17),
+  '\ud800',
+  'a\udc00b',
+  'abc\ud83d',
+];
+
+for (const input of inputs) {
+  const result = encoder.encode(input);
+  const expected = Buffer.from(input, 'utf8');
+  assert.strictEqual(Object.getPrototypeOf(result), Uint8Array.prototype);
+  assert.strictEqual(result.byteOffset, 0);
+  assert.strictEqual(result.buffer.byteLength, expected.length);
+  assert.deepStrictEqual(Buffer.from(result), expected);
+}