Array of object iteration strategies, benchmarked

iterator.bench.js

import { assert } from 'jsr:@std/assert'

const COUNT = 8
const ar = []
for (let i = 0; i < COUNT; ++i) {
  ar.push({ x: Math.random() * 1000 })
}
const sum = ar.reduce((a, obj) => (a + obj.x), 0)

function mapX() {
  return ar.map((obj) => obj.x)
}
Deno.bench('ar.map(o=>o.x)', () => {
  let s = 0
  for (const x of mapX()) {
    s += x
  }
  assert(s === sum)
})
function arrayFrom() {
  return Array.from(ar, (obj) => obj.x)
}
Deno.bench('Array.from(ar,o=>o.x)', () => {
  let s = 0
  for (let x of arrayFrom()) {
    s += x
  }
  assert(s === sum)
})
function* generateXs(a) {
  for (const o of a) {
    yield o.x
  }
}
Deno.bench('generator yield', () => {
  let s = 0
  for (const x of generateXs(ar)) {
    s += x
  }
  assert(s === sum)
})

function visitX(fn) {
  ar.forEach((o) => fn(o.x))
}
Deno.bench('visitor (ar.forEach(o=>fn(o.x))', () => {
  let s = 0
  visitX((x) => {
    s += x
  })
  assert(s === sum)
})
function arFromLoopPush() {
  const result = []
  for (const a of ar) {
    result.push(a.x)
  }
  return result
}
Deno.bench('copy array', () => {
  let s = 0
  for (const x of arFromLoopPush()) {
    s += x
  }
  assert(s === sum)
})

function iterateX(a) {
  return {
    [Symbol.iterator]: () => {
      const innerIt = a[Symbol.iterator]()
      return {
        next: () => {
          const innerNext = innerIt.next()
          return {
            done: innerNext.done,
            value: innerNext.value?.x,
          }
        },
      }
    },
  }
}

Deno.bench('x iterator', () => {
  let s = 0
  for (const x of iterateX(ar)) {
    s += x
  }
  assert(s === sum)
})

deno bench iterator.bench.js
    CPU | Apple M3
Runtime | Deno 2.0.3 (aarch64-apple-darwin)

file:///Users/dan/Source/MiniProjects/iterator.bench.js

benchmark                         time/iter (avg)        iter/s      (min … max)           p75      p99     p995
--------------------------------- ----------------------------- --------------------- --------------------------
ar.map(o=>o.x)                            46.6 ns    21,480,000 ( 40.7 ns …  76.0 ns)  48.9 ns  56.3 ns  60.8 ns
Array.from(ar,o=>o.x)                    286.9 ns     3,485,000 (272.2 ns … 313.5 ns) 290.9 ns 308.8 ns 313.5 ns
generator yield                          193.0 ns     5,181,000 (179.7 ns … 214.9 ns) 196.2 ns 208.8 ns 210.8 ns
visitor (ar.forEach(o=>fn(o.x))           32.8 ns    30,450,000 ( 25.1 ns …   1.7 µs)  32.1 ns  42.5 ns  57.6 ns
copy array                                34.7 ns    28,800,000 ( 28.8 ns … 342.4 ns)  35.7 ns  52.1 ns  61.0 ns
x iterator                               222.4 ns     4,496,000 (211.8 ns … 246.4 ns) 226.7 ns 239.7 ns 243.1 ns