lookupPerf.js

const { PerformanceObserver, performance } = require("perf_hooks")

// Parse useful information from performance events
const obs = new PerformanceObserver(items => {
  console.log(items.getEntries().map(e => `${e.name} : ${e.duration}`))
  performance.clearMarks()
})
obs.observe({ entryTypes: ["measure"] })

// Big array for big work
const arr = new Array(5000).fill(0).map((_, i) => i + 1)

// Build lookup object using reduce, object literal and spread syntax
performance.mark("A")

const lookup = arr.reduce((o, v, i) => ({ [v]: i, ...o }), {})

performance.mark("B")
performance.measure("Reduce lookup build", "A", "B")

// Build lookup object like an old fart with a for loop
performance.mark("C")

const lookup2 = {}
arr.forEach((v, i) => (lookup2[v] = i))

performance.mark("D")
performance.measure("Sane lookup build", "C", "D")

// Build lookup object with reduce, but Object.assign instead of spread
performance.mark("E")

const lookup3 = arr.reduce((o, v, i) => Object.assign(o, { [v]: i }), {})

performance.mark("F")
performance.measure("Compromise?", "E", "F")

// Ugliest reduce possible
performance.mark("G")

const lookup4 = arr.reduce((o, v, i) => {
  o[v] = i
  return o
}, {})

performance.mark("H")
performance.measure("Yes", "G", "H")