README.md

Benchmarking the code change in gatsbyjs/gatsby#7909

Example results on my machine:

//  Model Name:	MacBook Pro
//  Model Identifier:	MacBookPro14,3
//  Processor Name:	Intel Core i7
//  Processor Speed:	2.8 GHz
//  Number of Processors:	1
//  Total Number of Cores:	4
//  Memory:	16 GB

Starting benchmark

Array#includes => true (first item) x 90,527,340 ops/sec ±0.64% (84 runs sampled)
Array#includes => true (last item) x 48,148,045 ops/sec ±0.65% (88 runs sampled)
Array#includes => false x 44,982,781 ops/sec ±1.19% (88 runs sampled)
object property access => true (first item) x 555,733,626 ops/sec ±0.62% (83 runs sampled)
object property access => true (last item) x 565,248,917 ops/sec ±0.53% (90 runs sampled)
object property access => false x 553,660,965 ops/sec ±0.71% (89 runs sampled)
Set#has => true (first item) x 88,575,457 ops/sec ±1.15% (81 runs sampled)
Set#has => true (last item) x 93,230,253 ops/sec ±0.68% (89 runs sampled)
Set#has => false x 64,147,568 ops/sec ±0.53% (87 runs sampled)
Map#get => true (first item) x 579,591,059 ops/sec ±0.63% (87 runs sampled)
Map#get => true (last item) x 573,527,387 ops/sec ±0.64% (86 runs sampled)
Map#get => false x 581,403,037 ops/sec ±0.49% (91 runs sampled)

Fastest:
- Map#get => false
- Map#get => true (first item)

index.js

#!/usr/bin/env node

const Benchmark = require("benchmark");

const suite = new Benchmark.Suite();

const supportedExtensionsArray = [`jpeg`, `jpg`, `png`, `webp`, `tif`, `tiff`];
const supportedExtensionsObject = {
  jpeg: true,
  jpg: true,
  png: true,
  webp: true,
  tif: true,
  tiff: true
};
const supportedExtensionsMap = new Map(
  supportedExtensionsArray.map(ext => [ext, true])
);
const supportedExtensionsSet = new Set(supportedExtensionsArray);

suite
  .add("Array#includes => true (first item)", function() {
    supportedExtensionsArray.includes("jpeg");
  })
  .add("Array#includes => true (last item)", function() {
    supportedExtensionsArray.includes("tiff");
  })
  .add("Array#includes => false", function() {
    supportedExtensionsArray.includes("");
  })
  .add("object property access => true (first item)", function() {
    supportedExtensionsObject["jpeg"];
  })
  .add("object property access => true (last item)", function() {
    supportedExtensionsObject["tiff"];
  })
  .add("object property access => false", function() {
    supportedExtensionsObject[""];
  })
  .add("Set#has => true (first item)", function() {
    supportedExtensionsSet.has("jpeg");
  })
  .add("Set#has => true (last item)", function() {
    supportedExtensionsSet.has("tiff");
  })
  .add("Set#has => false", function() {
    supportedExtensionsSet.has("");
  })
  .add("Map#get => true (first item)", function() {
    supportedExtensionsMap.get("jpeg");
  })
  .add("Map#get => true (last item)", function() {
    supportedExtensionsMap.get("tiff");
  })
  .add("Map#get => false", function() {
    supportedExtensionsMap.get("");
  })
  .on("start", function() {
    console.log("Starting benchmark");
    console.log();
  })
  .on("cycle", function(event) {
    console.log(String(event.target));
  })
  .on("complete", function() {
    const fastest = this.filter("fastest")
      .map("name")
      .map(name => `- ${name}`)
      .join("\n");
    console.log();
    console.log("Fastest:");
    console.log(fastest);
  })
  .run({ async: true });

package.json

{
  "name": "gatsby-pr-7909-benchmark", 
  "version": "0.0.0", 
  "bin": "./index.js",
  "dependencies": {
    "benchmark": "^2.1.4",
    "node": "^10.0.0"
  }
}