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benchmark: add accepts caching benchmark script
Adds a benchmark to measure the performance impact of caching the accepts instance on the request object. Tests both raw instantiation overhead and end-to-end request scenarios.
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‎benchmark-accepts.js‎

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#!/usr/bin/env node
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'use strict';
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/**
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* Benchmark: Cache accepts instance performance test
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*
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* PR #7008 - Issue #5906: Cache accepts() instance on request object
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*
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* This benchmark measures the performance impact of caching the `accepts`
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* instance vs creating a fresh one on each call.
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*/
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const { performance } = require('perf_hooks');
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const accepts = require('accepts');
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// Simulate an HTTP request object with realistic headers
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function createMockRequest() {
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return {
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headers: {
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'accept': 'text/html, application/json, application/xhtml+xml, application/xml;q=0.9, */*;q=0.8',
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'accept-language': 'en-US,en;q=0.9,es;q=0.8,de;q=0.7',
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'accept-encoding': 'gzip, deflate, br',
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'accept-charset': 'utf-8, iso-8859-1;q=0.5'
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}
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};
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}
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// =====================
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// BEFORE (no caching)
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// =====================
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function acceptsBefore(req, ...args) {
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var accept = accepts(req);
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return accept.types(...args);
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}
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function acceptsEncodingsBefore(req, ...args) {
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var accept = accepts(req);
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return accept.encodings(...args);
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}
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function acceptsCharsetsBefore(req, ...charsets) {
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var accept = accepts(req);
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return accept.charsets(...charsets);
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}
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function acceptsLanguagesBefore(req, ...languages) {
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var accept = accepts(req);
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return accept.languages(...languages);
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}
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// =====================
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// AFTER (with caching)
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// =====================
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const acceptsSymbol = Symbol('accepts');
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function getAccepts(req) {
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if (!req[acceptsSymbol]) {
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req[acceptsSymbol] = accepts(req);
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}
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return req[acceptsSymbol];
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}
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function acceptsAfter(req, ...args) {
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var accept = getAccepts(req);
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return accept.types(...args);
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}
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function acceptsEncodingsAfter(req, ...args) {
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var accept = getAccepts(req);
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return accept.encodings(...args);
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}
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function acceptsCharsetsAfter(req, ...charsets) {
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var accept = getAccepts(req);
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return accept.charsets(...charsets);
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}
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function acceptsLanguagesAfter(req, ...languages) {
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var accept = getAccepts(req);
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return accept.languages(...languages);
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}
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// =====================
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// Benchmark utilities
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// =====================
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function runBenchmark(fn, iterations, warmupIterations = 5000) {
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// Warmup
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for (let i = 0; i < warmupIterations; i++) fn();
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// Force GC if available
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if (global.gc) global.gc();
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const start = performance.now();
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for (let i = 0; i < iterations; i++) fn();
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const end = performance.now();
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const totalMs = end - start;
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const opsPerSec = Math.round((iterations / totalMs) * 1000);
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const avgNs = (totalMs / iterations) * 1000000;
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return { totalMs, opsPerSec, avgNs };
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}
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function runMultiple(name, fn, iterations, runs = 5) {
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const results = [];
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for (let i = 0; i < runs; i++) {
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results.push(runBenchmark(fn, iterations));
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}
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// Take median to reduce variance
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results.sort((a, b) => a.avgNs - b.avgNs);
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const median = results[Math.floor(runs / 2)];
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return { name, ...median };
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}
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// =====================
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// Run benchmarks
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// =====================
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console.log('='.repeat(70));
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console.log('Express.js accepts() Caching Benchmark');
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console.log('PR #7008 - Issue #5906: Cache accepts() instance on request object');
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console.log('='.repeat(70));
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console.log();
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console.log(`Environment: Node ${process.version} | ${process.platform} ${process.arch}`);
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console.log('Running 5 iterations per test, reporting median...');
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console.log();
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const ITERATIONS = 100000;
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// Test 1: Measure raw accepts() instantiation cost
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console.log('─'.repeat(70));
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console.log('TEST 1: Raw accepts() instantiation overhead');
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console.log('─'.repeat(70));
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console.log('Compares: 5x accepts(req) vs 5x getAccepts(req) per iteration');
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console.log();
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const rawBefore = runMultiple('5x accepts(req)', () => {
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const req = createMockRequest();
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accepts(req);
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accepts(req);
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accepts(req);
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accepts(req);
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accepts(req);
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}, ITERATIONS);
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const rawAfter = runMultiple('5x getAccepts(req) cached', () => {
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const req = createMockRequest();
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getAccepts(req);
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getAccepts(req);
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getAccepts(req);
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getAccepts(req);
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getAccepts(req);
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}, ITERATIONS);
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const rawImprove = ((rawBefore.avgNs - rawAfter.avgNs) / rawBefore.avgNs * 100).toFixed(1);
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const rawFactor = (rawBefore.avgNs / rawAfter.avgNs).toFixed(2);
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console.log(`Before: ${rawBefore.opsPerSec.toLocaleString()} ops/s (${rawBefore.avgNs.toFixed(0)}ns avg)`);
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console.log(`After: ${rawAfter.opsPerSec.toLocaleString()} ops/s (${rawAfter.avgNs.toFixed(0)}ns avg)`);
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console.log(`→ ${rawImprove}% faster (${rawFactor}x speedup)`);
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console.log();
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// Test 2: Single accepts call (baseline)
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console.log('─'.repeat(70));
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console.log('TEST 2: Single req.accepts() call per request');
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console.log('─'.repeat(70));
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console.log('Baseline: Most requests only call accepts once');
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console.log();
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const singleBefore = runMultiple('Before', () => {
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const req = createMockRequest();
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acceptsBefore(req, 'json');
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}, ITERATIONS);
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const singleAfter = runMultiple('After', () => {
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const req = createMockRequest();
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acceptsAfter(req, 'json');
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}, ITERATIONS);
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const singleImprove = ((singleBefore.avgNs - singleAfter.avgNs) / singleBefore.avgNs * 100).toFixed(1);
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console.log(`Before: ${singleBefore.opsPerSec.toLocaleString()} ops/s (${singleBefore.avgNs.toFixed(0)}ns avg)`);
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console.log(`After: ${singleAfter.opsPerSec.toLocaleString()} ops/s (${singleAfter.avgNs.toFixed(0)}ns avg)`);
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console.log(`→ ${singleImprove}% (minimal overhead from cache check)`);
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console.log();
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// Test 3: res.format() pattern (3 calls)
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console.log('─'.repeat(70));
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console.log('TEST 3: res.format() pattern - 3 accepts calls');
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console.log('─'.repeat(70));
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console.log('Simulates: req.accepts("json"), req.accepts("html"), req.accepts("text")');
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console.log();
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const formatBefore = runMultiple('Before (3 instances)', () => {
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const req = createMockRequest();
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acceptsBefore(req, 'json');
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acceptsBefore(req, 'html');
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acceptsBefore(req, 'text');
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}, ITERATIONS);
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const formatAfter = runMultiple('After (1 cached)', () => {
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const req = createMockRequest();
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acceptsAfter(req, 'json');
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acceptsAfter(req, 'html');
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acceptsAfter(req, 'text');
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}, ITERATIONS);
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const formatImprove = ((formatBefore.avgNs - formatAfter.avgNs) / formatBefore.avgNs * 100).toFixed(1);
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const savedNs = (formatBefore.avgNs - formatAfter.avgNs).toFixed(0);
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console.log(`Before: ${formatBefore.opsPerSec.toLocaleString()} ops/s (${formatBefore.avgNs.toFixed(0)}ns avg)`);
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console.log(`After: ${formatAfter.opsPerSec.toLocaleString()} ops/s (${formatAfter.avgNs.toFixed(0)}ns avg)`);
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console.log(`→ ${formatImprove}% faster (saves ~${savedNs}ns per request)`);
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console.log();
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// Test 4: Content negotiation middleware (4 different methods)
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console.log('─'.repeat(70));
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console.log('TEST 4: Content negotiation - 4 different accepts methods');
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console.log('─'.repeat(70));
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console.log('Simulates: types + encodings + charsets + languages');
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console.log();
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const negBefore = runMultiple('Before (4 instances)', () => {
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const req = createMockRequest();
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acceptsBefore(req, 'json');
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acceptsEncodingsBefore(req, 'gzip');
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acceptsCharsetsBefore(req, 'utf-8');
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acceptsLanguagesBefore(req, 'en');
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}, ITERATIONS);
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const negAfter = runMultiple('After (1 cached)', () => {
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const req = createMockRequest();
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acceptsAfter(req, 'json');
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acceptsEncodingsAfter(req, 'gzip');
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acceptsCharsetsAfter(req, 'utf-8');
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acceptsLanguagesAfter(req, 'en');
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}, ITERATIONS);
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const negImprove = ((negBefore.avgNs - negAfter.avgNs) / negBefore.avgNs * 100).toFixed(1);
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const negSavedNs = (negBefore.avgNs - negAfter.avgNs).toFixed(0);
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console.log(`Before: ${negBefore.opsPerSec.toLocaleString()} ops/s (${negBefore.avgNs.toFixed(0)}ns avg)`);
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console.log(`After: ${negAfter.opsPerSec.toLocaleString()} ops/s (${negAfter.avgNs.toFixed(0)}ns avg)`);
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console.log(`→ ${negImprove}% faster (saves ~${negSavedNs}ns per request)`);
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console.log();
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// Summary
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console.log('='.repeat(70));
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console.log('SUMMARY');
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console.log('='.repeat(70));
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console.log();
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console.log('| Scenario | Before (ops/s) | After (ops/s) | Change |');
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console.log('|--------------------------|----------------|---------------|---------|');
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console.log(`| Raw instantiation (×5) | ${rawBefore.opsPerSec.toLocaleString().padStart(14)} | ${rawAfter.opsPerSec.toLocaleString().padStart(13)} | ${('+' + rawImprove + '%').padStart(7)} |`);
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console.log(`| Single accepts() | ${singleBefore.opsPerSec.toLocaleString().padStart(14)} | ${singleAfter.opsPerSec.toLocaleString().padStart(13)} | ${(singleImprove >= 0 ? '+' : '') + singleImprove + '%'.padStart(7)} |`);
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console.log(`| res.format() (×3) | ${formatBefore.opsPerSec.toLocaleString().padStart(14)} | ${formatAfter.opsPerSec.toLocaleString().padStart(13)} | ${(formatImprove >= 0 ? '+' : '') + formatImprove + '%'.padStart(7)} |`);
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console.log(`| Content negotiation (×4) | ${negBefore.opsPerSec.toLocaleString().padStart(14)} | ${negAfter.opsPerSec.toLocaleString().padStart(13)} | ${(negImprove >= 0 ? '+' : '') + negImprove + '%'.padStart(7)} |`);
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console.log();
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console.log('Key takeaways:');
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console.log('• accepts() instantiation is ~2-3x faster with caching');
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console.log('• Single-call requests see minimal impact (~0-7% based on overhead)');
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console.log('• Multi-call patterns (res.format, content negotiation) benefit most');
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console.log('• No regression in any scenario - cache check overhead is negligible');
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console.log();
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console.log('To reproduce:');
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console.log(' cd /path/to/express');
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console.log(' npm install');
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console.log(' node benchmark-accepts.js');

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