Benchmarking spread inside a loop

data.js

module.exports = [
  {
    country: "Afghanistan",
    continent: "Asia",
  },
  {
    country: "Albania",
    continent: "Europe",
  },
  {
    country: "Algeria",
    continent: "Africa",
  },
  {
    country: "American Samoa",
    continent: "Oceania",
  },
  {
    country: "Andorra",
    continent: "Europe",
  },
  {
    country: "Angola",
    continent: "Africa",
  },
  {
    country: "Anguilla",
    continent: "North America",
  },
  {
    country: "Antarctica",
    continent: "Antarctica",
  },
  {
    country: "Antigua and Barbuda",
    continent: "North America",
  },
  {
    country: "Argentina",
    continent: "South America",
  },
  {
    country: "Armenia",
    continent: "Asia",
  },
  {
    country: "Aruba",
    continent: "North America",
  },
  {
    country: "Australia",
    continent: "Oceania",
  },
  {
    country: "Austria",
    continent: "Europe",
  },
  {
    country: "Azerbaijan",
    continent: "Asia",
  },
  {
    country: "Bahamas",
    continent: "North America",
  },
  {
    country: "Bahrain",
    continent: "Asia",
  },
  {
    country: "Bangladesh",
    continent: "Asia",
  },
  {
    country: "Barbados",
    continent: "North America",
  },
  {
    country: "Belarus",
    continent: "Europe",
  },
  {
    country: "Belgium",
    continent: "Europe",
  },
  {
    country: "Belize",
    continent: "North America",
  },
  {
    country: "Benin",
    continent: "Africa",
  },
  {
    country: "Bermuda",
    continent: "North America",
  },
  {
    country: "Bhutan",
    continent: "Asia",
  },
  {
    country: "Bolivia",
    continent: "South America",
  },
  {
    country: "Bosnia and Herzegovina",
    continent: "Europe",
  },
  {
    country: "Botswana",
    continent: "Africa",
  },
  {
    country: "Bouvet Island",
    continent: "Antarctica",
  },
  {
    country: "Brazil",
    continent: "South America",
  },
  {
    country: "British Indian Ocean Territory",
    continent: "Africa",
  },
  {
    country: "Brunei",
    continent: "Asia",
  },
  {
    country: "Bulgaria",
    continent: "Europe",
  },
  {
    country: "Burkina Faso",
    continent: "Africa",
  },
  {
    country: "Burundi",
    continent: "Africa",
  },
  {
    country: "Cambodia",
    continent: "Asia",
  },
  {
    country: "Cameroon",
    continent: "Africa",
  },
  {
    country: "Canada",
    continent: "North America",
  },
  {
    country: "Cape Verde",
    continent: "Africa",
  },
  {
    country: "Cayman Islands",
    continent: "North America",
  },
  {
    country: "Central African Republic",
    continent: "Africa",
  },
  {
    country: "Chad",
    continent: "Africa",
  },
  {
    country: "Chile",
    continent: "South America",
  },
  {
    country: "China",
    continent: "Asia",
  },
  {
    country: "Christmas Island",
    continent: "Oceania",
  },
  {
    country: "Cocos (Keeling) Islands",
    continent: "Oceania",
  },
  {
    country: "Colombia",
    continent: "South America",
  },
  {
    country: "Comoros",
    continent: "Africa",
  },
  {
    country: "Congo",
    continent: "Africa",
  },
  {
    country: "Cook Islands",
    continent: "Oceania",
  },
  {
    country: "Costa Rica",
    continent: "North America",
  },
  {
    country: "Croatia",
    continent: "Europe",
  },
  {
    country: "Cuba",
    continent: "North America",
  },
  {
    country: "Cyprus",
    continent: "Asia",
  },
  {
    country: "Czech Republic",
    continent: "Europe",
  },
  {
    country: "Denmark",
    continent: "Europe",
  },
  {
    country: "Djibouti",
    continent: "Africa",
  },
  {
    country: "Dominica",
    continent: "North America",
  },
  {
    country: "Dominican Republic",
    continent: "North America",
  },
  {
    country: "East Timor",
    continent: "Asia",
  },
  {
    country: "Ecuador",
    continent: "South America",
  },
  {
    country: "Egypt",
    continent: "Africa",
  },
  {
    country: "El Salvador",
    continent: "North America",
  },
  {
    country: "England",
    continent: "Europe",
  },
  {
    country: "Equatorial Guinea",
    continent: "Africa",
  },
  {
    country: "Eritrea",
    continent: "Africa",
  },
  {
    country: "Estonia",
    continent: "Europe",
  },
  {
    country: "Ethiopia",
    continent: "Africa",
  },
  {
    country: "Falkland Islands",
    continent: "South America",
  },
  {
    country: "Faroe Islands",
    continent: "Europe",
  },
  {
    country: "Fiji Islands",
    continent: "Oceania",
  },
  {
    country: "Finland",
    continent: "Europe",
  },
  {
    country: "France",
    continent: "Europe",
  },
  {
    country: "French Guiana",
    continent: "South America",
  },
  {
    country: "French Polynesia",
    continent: "Oceania",
  },
  {
    country: "French Southern territories",
    continent: "Antarctica",
  },
  {
    country: "Gabon",
    continent: "Africa",
  },
  {
    country: "Gambia",
    continent: "Africa",
  },
  {
    country: "Georgia",
    continent: "Asia",
  },
  {
    country: "Germany",
    continent: "Europe",
  },
  {
    country: "Ghana",
    continent: "Africa",
  },
  {
    country: "Gibraltar",
    continent: "Europe",
  },
  {
    country: "Greece",
    continent: "Europe",
  },
  {
    country: "Greenland",
    continent: "North America",
  },
  {
    country: "Grenada",
    continent: "North America",
  },
  {
    country: "Guadeloupe",
    continent: "North America",
  },
  {
    country: "Guam",
    continent: "Oceania",
  },
  {
    country: "Guatemala",
    continent: "North America",
  },
  {
    country: "Guinea",
    continent: "Africa",
  },
  {
    country: "Guinea-Bissau",
    continent: "Africa",
  },
  {
    country: "Guyana",
    continent: "South America",
  },
  {
    country: "Haiti",
    continent: "North America",
  },
  {
    country: "Heard Island and McDonald Islands",
    continent: "Antarctica",
  },
  {
    country: "Holy See (Vatican City State)",
    continent: "Europe",
  },
  {
    country: "Honduras",
    continent: "North America",
  },
  {
    country: "Hong Kong",
    continent: "Asia",
  },
  {
    country: "Hungary",
    continent: "Europe",
  },
  {
    country: "Iceland",
    continent: "Europe",
  },
  {
    country: "India",
    continent: "Asia",
  },
  {
    country: "Indonesia",
    continent: "Asia",
  },
  {
    country: "Iran",
    continent: "Asia",
  },
  {
    country: "Iraq",
    continent: "Asia",
  },
  {
    country: "Ireland",
    continent: "Europe",
  },
  {
    country: "Israel",
    continent: "Asia",
  },
  {
    country: "Italy",
    continent: "Europe",
  },
  {
    country: "Ivory Coast",
    continent: "Africa",
  },
  {
    country: "Jamaica",
    continent: "North America",
  },
  {
    country: "Japan",
    continent: "Asia",
  },
  {
    country: "Jordan",
    continent: "Asia",
  },
  {
    country: "Kazakhstan",
    continent: "Asia",
  },
  {
    country: "Kenya",
    continent: "Africa",
  },
  {
    country: "Kiribati",
    continent: "Oceania",
  },
  {
    country: "Kuwait",
    continent: "Asia",
  },
  {
    country: "Kyrgyzstan",
    continent: "Asia",
  },
  {
    country: "Laos",
    continent: "Asia",
  },
  {
    country: "Latvia",
    continent: "Europe",
  },
  {
    country: "Lebanon",
    continent: "Asia",
  },
  {
    country: "Lesotho",
    continent: "Africa",
  },
  {
    country: "Liberia",
    continent: "Africa",
  },
  {
    country: "Libyan Arab Jamahiriya",
    continent: "Africa",
  },
  {
    country: "Liechtenstein",
    continent: "Europe",
  },
  {
    country: "Lithuania",
    continent: "Europe",
  },
  {
    country: "Luxembourg",
    continent: "Europe",
  },
  {
    country: "Macao",
    continent: "Asia",
  },
  {
    country: "North Macedonia",
    continent: "Europe",
  },
  {
    country: "Madagascar",
    continent: "Africa",
  },
  {
    country: "Malawi",
    continent: "Africa",
  },
  {
    country: "Malaysia",
    continent: "Asia",
  },
  {
    country: "Maldives",
    continent: "Asia",
  },
  {
    country: "Mali",
    continent: "Africa",
  },
  {
    country: "Malta",
    continent: "Europe",
  },
  {
    country: "Marshall Islands",
    continent: "Oceania",
  },
  {
    country: "Martinique",
    continent: "North America",
  },
  {
    country: "Mauritania",
    continent: "Africa",
  },
  {
    country: "Mauritius",
    continent: "Africa",
  },
  {
    country: "Mayotte",
    continent: "Africa",
  },
  {
    country: "Mexico",
    continent: "North America",
  },
  {
    country: "Micronesia, Federated States of",
    continent: "Oceania",
  },
  {
    country: "Moldova",
    continent: "Europe",
  },
  {
    country: "Monaco",
    continent: "Europe",
  },
  {
    country: "Mongolia",
    continent: "Asia",
  },
  {
    country: "Montenegro",
    continent: "Europe",
  },
  {
    country: "Montserrat",
    continent: "North America",
  },
  {
    country: "Morocco",
    continent: "Africa",
  },
  {
    country: "Mozambique",
    continent: "Africa",
  },
  {
    country: "Myanmar",
    continent: "Asia",
  },
  {
    country: "Namibia",
    continent: "Africa",
  },
  {
    country: "Nauru",
    continent: "Oceania",
  },
  {
    country: "Nepal",
    continent: "Asia",
  },
  {
    country: "Netherlands",
    continent: "Europe",
  },
  {
    country: "Netherlands Antilles",
    continent: "North America",
  },
  {
    country: "New Caledonia",
    continent: "Oceania",
  },
  {
    country: "New Zealand",
    continent: "Oceania",
  },
  {
    country: "Nicaragua",
    continent: "North America",
  },
  {
    country: "Niger",
    continent: "Africa",
  },
  {
    country: "Nigeria",
    continent: "Africa",
  },
  {
    country: "Niue",
    continent: "Oceania",
  },
  {
    country: "Norfolk Island",
    continent: "Oceania",
  },
  {
    country: "North Korea",
    continent: "Asia",
  },
  {
    country: "Northern Ireland",
    continent: "Europe",
  },
  {
    country: "Northern Mariana Islands",
    continent: "Oceania",
  },
  {
    country: "Norway",
    continent: "Europe",
  },
  {
    country: "Oman",
    continent: "Asia",
  },
  {
    country: "Pakistan",
    continent: "Asia",
  },
  {
    country: "Palau",
    continent: "Oceania",
  },
  {
    country: "Palestine",
    continent: "Asia",
  },
  {
    country: "Panama",
    continent: "North America",
  },
  {
    country: "Papua New Guinea",
    continent: "Oceania",
  },
  {
    country: "Paraguay",
    continent: "South America",
  },
  {
    country: "Peru",
    continent: "South America",
  },
  {
    country: "Philippines",
    continent: "Asia",
  },
  {
    country: "Pitcairn",
    continent: "Oceania",
  },
  {
    country: "Poland",
    continent: "Europe",
  },
  {
    country: "Portugal",
    continent: "Europe",
  },
  {
    country: "Puerto Rico",
    continent: "North America",
  },
  {
    country: "Qatar",
    continent: "Asia",
  },
  {
    country: "Reunion",
    continent: "Africa",
  },
  {
    country: "Romania",
    continent: "Europe",
  },
  {
    country: "Russian Federation",
    continent: "Europe",
  },
  {
    country: "Rwanda",
    continent: "Africa",
  },
  {
    country: "Saint Helena",
    continent: "Africa",
  },
  {
    country: "Saint Kitts and Nevis",
    continent: "North America",
  },
  {
    country: "Saint Lucia",
    continent: "North America",
  },
  {
    country: "Saint Pierre and Miquelon",
    continent: "North America",
  },
  {
    country: "Saint Vincent and the Grenadines",
    continent: "North America",
  },
  {
    country: "Samoa",
    continent: "Oceania",
  },
  {
    country: "San Marino",
    continent: "Europe",
  },
  {
    country: "Sao Tome and Principe",
    continent: "Africa",
  },
  {
    country: "Saudi Arabia",
    continent: "Asia",
  },
  {
    country: "Scotland",
    continent: "Europe",
  },
  {
    country: "Senegal",
    continent: "Africa",
  },
  {
    country: "Serbia",
    continent: "Europe",
  },
  {
    country: "Seychelles",
    continent: "Africa",
  },
  {
    country: "Sierra Leone",
    continent: "Africa",
  },
  {
    country: "Singapore",
    continent: "Asia",
  },
  {
    country: "Slovakia",
    continent: "Europe",
  },
  {
    country: "Slovenia",
    continent: "Europe",
  },
  {
    country: "Solomon Islands",
    continent: "Oceania",
  },
  {
    country: "Somalia",
    continent: "Africa",
  },
  {
    country: "South Africa",
    continent: "Africa",
  },
  {
    country: "South Georgia and the South Sandwich Islands",
    continent: "Antarctica",
  },
  {
    country: "South Korea",
    continent: "Asia",
  },
  {
    country: "South Sudan",
    continent: "Africa",
  },
  {
    country: "Spain",
    continent: "Europe",
  },
  {
    country: "Sri Lanka",
    continent: "Asia",
  },
  {
    country: "Sudan",
    continent: "Africa",
  },
  {
    country: "Suriname",
    continent: "South America",
  },
  {
    country: "Svalbard and Jan Mayen",
    continent: "Europe",
  },
  {
    country: "Swaziland",
    continent: "Africa",
  },
  {
    country: "Sweden",
    continent: "Europe",
  },
  {
    country: "Switzerland",
    continent: "Europe",
  },
  {
    country: "Syria",
    continent: "Asia",
  },
  {
    country: "Tajikistan",
    continent: "Asia",
  },
  {
    country: "Tanzania",
    continent: "Africa",
  },
  {
    country: "Thailand",
    continent: "Asia",
  },
  {
    country: "The Democratic Republic of Congo",
    continent: "Africa",
  },
  {
    country: "Togo",
    continent: "Africa",
  },
  {
    country: "Tokelau",
    continent: "Oceania",
  },
  {
    country: "Tonga",
    continent: "Oceania",
  },
  {
    country: "Trinidad and Tobago",
    continent: "North America",
  },
  {
    country: "Tunisia",
    continent: "Africa",
  },
  {
    country: "Turkey",
    continent: "Asia",
  },
  {
    country: "Turkmenistan",
    continent: "Asia",
  },
  {
    country: "Turks and Caicos Islands",
    continent: "North America",
  },
  {
    country: "Tuvalu",
    continent: "Oceania",
  },
  {
    country: "Uganda",
    continent: "Africa",
  },
  {
    country: "Ukraine",
    continent: "Europe",
  },
  {
    country: "United Arab Emirates",
    continent: "Asia",
  },
  {
    country: "United Kingdom",
    continent: "Europe",
  },
  {
    country: "United States",
    continent: "North America",
  },
  {
    country: "United States Minor Outlying Islands",
    continent: "Oceania",
  },
  {
    country: "Uruguay",
    continent: "South America",
  },
  {
    country: "Uzbekistan",
    continent: "Asia",
  },
  {
    country: "Vanuatu",
    continent: "Oceania",
  },
  {
    country: "Venezuela",
    continent: "South America",
  },
  {
    country: "Vietnam",
    continent: "Asia",
  },
  {
    country: "Virgin Islands, British",
    continent: "North America",
  },
  {
    country: "Virgin Islands, U.S.",
    continent: "North America",
  },
  {
    country: "Wales",
    continent: "Europe",
  },
  {
    country: "Wallis and Futuna",
    continent: "Oceania",
  },
  {
    country: "Western Sahara",
    continent: "Africa",
  },
  {
    country: "Yemen",
    continent: "Asia",
  },
  {
    country: "Zambia",
    continent: "Africa",
  },
  {
    country: "Zimbabwe",
    continent: "Africa",
  },
];

package.json

{
  "name": "obj-spread-test",
  "version": "1.0.0",
  "description": "",
  "main": "suite.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "keywords": [],
  "author": "",
  "license": "ISC",
  "dependencies": {
    "benchmark": "^2.1.4"
  }
}

suite.js

const countries = require("./data");

const benchmark = require("benchmark");

const suite = new benchmark.Suite();

suite
  .add(".forEach() with external variable", function () {
    const result = {};

    countries.forEach(({ name, continent }) => {
      if (Array.isArray(result[continent])) {
        result[continent].push(name)
      } else {
        result[continent] = [name]
      }
    });
  })
  .add(".reduce() with spread", function () {
    countries.reduce((acc, { name, continent }) => ({
      ...acc,
      [continent]: [...acc[continent] ?? [], name],
    }), {});
  })
  .add(".reduce() with assignment", function () {
    countries.reduce((acc, { name, continent }) => {
      acc[continent] ??= [];
      acc[continent].push(name);

      return acc;
    }, {});
  })
  .on("cycle", (event) => {
    console.log(" -", String(event.target));
  })
  .on("complete", function () {
    console.log("\nThe fastest is:", this.filter("fastest").map("name"));
  })
  .run({ async: false });