Node.js map/for performance benchmark comparison

README.md

Comparison of different way to map an array in Node.js

• Properly used map is quite good;

• Badly used for_i can be absolutely horrible;

• A custom map-like function is on par with bare for_i;

• Not all for_i loops are equally optimized;

• Node 10, 12 and 14 have the same overall picture;

• Arrow vs function callbacks - makes no significant difference.

Takeaway:

1. map is the way to go most of the times, arrow or function callback - doesn't matter;
2. No need to write bare for_i loops everywhere in the hot path - wrapper map-like function can be indistinguishable in performance;
3. Don't take anything for granted - test it. Not all for_i loops are equal.

index.js

// npm i benny
const b = require('benny');

function preallocCopy1 (src) {
  const res = new Array(src.length);
  for(var i=src.length; i-- > 0;) {
    res[i] = src[i];
  }
  return res;
}

function preallocMap1 (f, src) {
  const res = new Array(src.length);
  for(var i=src.length; i-- > 0;) {
    res[i] = f(src[i]);
  }
  return res;
}

function preallocCopy2 (src) {
  const res = new Array(src.length);
  for(var i=src.length; i > 0; i--) {
    res[i] = src[i];
  }
  return res;
}

function preallocMap2 (f, src) {
  const res = new Array(src.length);
  for(var i=src.length; i > 0; i--) {
    res[i] = f(src[i]);
  }
  return res;
}

function preallocCopy3 (src) {
  const len = src.length;
  const res = new Array(len);
  for(var i=0; i++ < len;) {
    res[i] = src[i];
  }
  return res;
}

function preallocMap3 (f, src) {
  const len = src.length;
  const res = new Array(len);
  for(var i=0; i++ < len;) {
    res[i] = f(src[i]);
  }
  return res;
}

function preallocCopy4 (src) {
  const len = src.length;
  const res = new Array(len);
  for(var i=0; i < len; i++) {
    res[i] = src[i];
  }
  return res;
}

function preallocMap4 (f, src) {
  const len = src.length;
  const res = new Array(len);
  for(var i=0; i < len; i++) {
    res[i] = f(src[i]);
  }
  return res;
}

const input = 'giyrxgfoyugrxeupqzuehfgfccsydgfpxwieuhqzuiehfuiegfyuegfpegrygrypiop634927chmiuqefdyiqdetfcityrfiwecfiuegciquegiyrxgfoyugrxeupqzuehfgfccsydgfpxwieuhqzuiehfuiegfyuegfpegrygrypiop634927chmiuqefdyiqdetfcityrfiwecfiuegciquegiyrxgfoyugrxeupqzuehfgfccsydgfpxwieuhqz'.split('');

b.suite(
  'map_for_etc',

  b.add('map(function ~ id)', () => {
    var output = input.map(function (x){ return x; });
  }),

  b.add('map(arrow ~ id)', () => {
    var output = input.map((x) => x);
  }),

  b.add('map(function ~ push)', () => {
    var output = [];
    input.map(function (x){ output.push(x); });
  }),

  b.add('map(arrow ~ push)', () => {
    var output = [];
    input.map((x) => output.push(x));
  }),

  b.add('forEach(function ~ push)', () => {
    var output = [];
    input.forEach(function (x){ output.push(x); });
  }),

  b.add('forEach(arrow ~ push)', () => {
    var output = [];
    input.forEach((x) => output.push(x));
  }),

  b.add('for_of(push)', () => {
    var output = [];
    for(const x of input) { output.push(x); }
  }),

  b.add('for_i1(push ~ backwards, combined)', () => {
    var output = [];
    for(let i = input.length; i-- > 0;) { output.push(input[i]); }
  }),

  b.add('for_i2(push ~ backwards)', () => {
    var output = [];
    for(let i = input.length; i > 0; i--) { output.push(input[i]); }
  }),

  b.add('for_i3(push ~ forward, combined)', () => {
    const len = input.length;
    var output = [];
    for(let i = 0; i++ < len;) { output.push(input[i]); }
  }),

  b.add('for_i4(push ~ forward)', () => {
    const len = input.length;
    var output = [];
    for(let i = 0; i < len; i++) { output.push(input[i]); }
  }),

  b.add('for_i1(preallocate ~ backwards, combined)', () => {
    const len = input.length;
    var output = new Array(len);
    for(let i = len; i-- > 0;) { output[i] = input[i]; }
  }),

  b.add('for_i2(preallocate ~ backwards)', () => {
    const len = input.length;
    var output = new Array(len);
    for(let i = len; i > 0; i--) { output[i] = input[i]; }
  }),

  b.add('for_i3(preallocate ~ forward, combined)', () => {
    const len = input.length;
    var output = new Array(len);
    for(let i = 0; i++ < len;) { output[i] = input[i]; }
  }),

  b.add('for_i4(preallocate ~ forward)', () => {
    const len = input.length;
    var output = new Array(len);
    for(let i = 0; i < len; i++) { output[i] = input[i]; }
  }),

  b.add('preallocCopy1( ~ backwards, combined)', () => {
    var output = preallocCopy1(input);
  }),

  b.add('preallocCopy2( ~ backwards)', () => {
    var output = preallocCopy2(input);
  }),

  b.add('preallocCopy3( ~ forward, combined)', () => {
    var output = preallocCopy3(input);
  }),

  b.add('preallocCopy4( ~ forward)', () => {
    var output = preallocCopy4(input);
  }),

  b.add('preallocMap1(id ~ backwards, combined)', () => {
    var output = preallocMap1((x) => x, input);
  }),

  b.add('preallocMap2(id ~ backwards)', () => {
    var output = preallocMap2((x) => x, input);
  }),

  b.add('preallocMap3(id ~ forward, combined)', () => {
    var output = preallocMap3((x) => x, input);
  }),

  b.add('preallocMap4(id ~ forward)', () => {
    var output = preallocMap4((x) => x, input);
  }),

  b.cycle(),
  b.complete(),
  b.save({ file: 'map_for_etc', format: 'json' }),
  b.save({ file: 'map_for_etc', format: 'csv' }),
  b.save({ file: 'map_for_etc', format: 'chart.html' }),
);

package.json

{
  "name": "map-for-benchmark",
  "version": "1.0.0",
  "main": "index.js",
  "scripts": {
    "test": "node ./index.js"
  },
  "devDependencies": {
    "benny": "^3.6.15"
  }
}

result.csv