get header use lowercase, 10x speed

header_get.js

'use strict';

const Benchmark = require('benchmark');
const benchmarks = require('beautify-benchmark');
const suite = new Benchmark.Suite();

suite
.add('get header all lower case', function() {
  const res = {};
  res['x-frame-options1'] = 'X-Frame-Options1 value';
  res['x-frame-options2'] = 'X-Frame-Options2 value';
  res['x-frame-options3'] = 'X-Frame-Options3 value';

  res['x-frame-options1'.toLowerCase()];
  res['x-frame-options2'.toLowerCase()];
  res['x-frame-options3'.toLowerCase()];
})

.add('get header mixed case', function() {
  const res = {};
  res['x-frame-options1'] = 'X-Frame-Options1 value';
  res['x-frame-options2'] = 'X-Frame-Options2 value';
  res['x-frame-options3'] = 'X-Frame-Options3 value';

  res['X-Frame-Options1'.toLowerCase()];
  res['X-Frame-Options2'.toLowerCase()];
  res['X-Frame-Options3'.toLowerCase()];
})
.on('cycle', event => {
  benchmarks.add(event.target);
})
.on('start', () => {
  console.log('\n  res.getHeader() Benchmark\n  node version: %s, date: %s\n  Starting...',
    process.version, Date());
})
.on('complete', () => {
  benchmarks.log();
})
.run({ async: false });

// res.getHeader() Benchmark
//  node version: v6.5.0, date: Mon Sep 12 2016 18:22:37 GMT+0800 (CST)
//  Starting...
//  2 tests completed.
//
//  get header all lower case x 7,139,523 ops/sec ±1.13% (85 runs sampled)
//  get header mixed case     x 1,222,787 ops/sec ±5.13% (76 runs sampled)