performanceOfMutableArrayOperations.js

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

const calculateWeight = (item) => {
  const random = Math.random();
  return Math.trunc(random * 1000);
};

const groupItemsByWeightImmutable = (items) =>
  items.reduce((acc, item) => {
    const weight = calculateWeight(item);
    const itemsList = [...(acc[weight] ?? []), item];

    return {
      ...acc,
      [weight]: itemsList,
    };
  }, {});

const groupItemsByWeightMutable = (items) =>
  items.reduce((acc, item) => {
    const weight = calculateWeight(item);
    acc[weight] = acc[weight] ?? [];
    acc[weight].push(item);

    return acc;
  }, {});

const main = () => {
  const observer = new PerformanceObserver((items) => {
    const measures = items
      .getEntries()
      .map((entry) => ({ name: entry.name, duration: entry.duration }));
    console.table(measures);
  });
  observer.observe({ type: "measure" });

  [groupItemsByWeightImmutable, groupItemsByWeightMutable].forEach(
    (groupItems) => {
      [1, 10, 100, 1_000, 10_000, 100_000, 1_000_000].forEach((length) => {
        const items = Array.from(new Array(length), () => null);
        const markName = `${groupItems.name}, ${length}`;

        performance.mark(markName);
        groupItems(items);
        performance.measure(
          `${markName} - Time to process ${length}`,
          markName
        );
      });
    }
  );
};

main();