Benchmark node.js array concatenation methods

array-bench.js

const Benchmark = require('benchmark');
const _ = require('lodash');
const assert = require('assert');

const saved = [];
for (let i = 0; i < 400; i += 1) {
  saved.push(i);
}
// Uncomment the asserts to verify that all tests are generating the same outputs
const goldStandard = saved.concat(saved);

let array1 = [];
let array2 = [];
let array3 = [];
const nonEmptyTemp = [1, 2];

const reset = () => {
  array1 = saved;
  array2 = saved;
  array3 = [];
};

const methods = {
  assignSpreadPush: () => {
    reset();
    array3 = [...array1];
    array3.push(...array2);
    // assert.ok(_.isEqual(array3, goldStandard));
  },
  concat: () => {
    reset();
    array3 = array1.concat(array2);
    // assert.ok(_.isEqual(array3, goldStandard));
  },
  concatSmall: () => {
    reset();
    array3 = [].concat(array1, array2);
    // assert.ok(_.isEqual(array3, goldStandard));
  },
  concatSmallInit: () => {
    reset();
    array3 = nonEmptyTemp.concat(array1, array2).slice(2);
    // assert.ok(_.isEqual(array3, goldStandard));
  },
  concatSpreadSmallInit: () => {
    reset();
    array3 = [...[1, 2], ...array1, ...array2].slice(2);
    // assert.ok(_.isEqual(array3, goldStandard));
  },
  push: () => {
    reset();
    array1.forEach(x => array3.push(x));
    array2.forEach(x => array3.push(x));
    // assert.ok(_.isEqual(array3, goldStandard));
  },
  pushClone: () => {
    reset();
    array3 = array1.slice(0);
    array2.forEach(x => array3.push(x));
    // assert.ok(_.isEqual(array3, goldStandard));
  },
  sliceSpreadPush: () => {
    reset();
    array3 = array1.slice(0);
    array3.push(...array2);
    // assert.ok(_.isEqual(array3, goldStandard));
  },
  spread: () => {
    reset();
    array3 = [...array1, ...array2];
    // assert.ok(_.isEqual(array3, goldStandard));
  },
  spreadInital: () => {
    reset();
    array3 = [1, 2, ...array1, ...array2].slice(2);
    // assert.ok(_.isEqual(array3, goldStandard));
  },
  spreadPush: () => {
    reset();
    array3.push(...array1);
    array3.push(...array2);
    // assert.ok(_.isEqual(array3, goldStandard));
  },
  spreadPushInlineInline: () => {
    reset();
    array3.push(...array1, ...array2);
    // assert.ok(_.isEqual(array3, goldStandard));
  },
  spreadPushInlineInlineInnerArray: () => {
    reset();
    array3.push(...[...array1, ...array2]);
    // assert.ok(_.isEqual(array3, goldStandard));
  },
};

console.log('Tests running...\n');
const suite = new Benchmark.Suite();
_.each(methods, (f, n) => suite.add(n, f));
suite.on('cycle', event => {
  console.log(String(event.target));
  console.log(`Memory: ${process.memoryUsage().heapUsed / 1024 / 1024} Mb\n`);
})
.on('complete', function complete() {
  console.log(`Fastest is ${this.filter('fastest').map('name')}`); // eslint-disable-line
})
.run({});