bun.sh/test/js/web/timers/performance.test.js

import { expect, it } from "bun:test";

it("performance.now() should be monotonic", () => {
  const first = performance.now();
  const second = performance.now();
  const third = performance.now();
  const fourth = performance.now();
  const fifth = performance.now();
  const sixth = performance.now();
  expect(first < second).toBe(true);
  expect(second < third).toBe(true);
  expect(third < fourth).toBe(true);
  expect(fourth < fifth).toBe(true);
  expect(fifth < sixth).toBe(true);
  expect(Bun.nanoseconds() > 0).toBe(true);
  expect(Bun.nanoseconds() > sixth).toBe(true);
  expect(typeof Bun.nanoseconds() === "number").toBe(true);
});

it("performance.timeOrigin + performance.now() should be similar to Date.now()", () => {
  expect(Math.abs(performance.timeOrigin + performance.now() - Date.now()) < 1000).toBe(true);
});

// https://github.com/oven-sh/bun/issues/5604
it("performance.now() DOMJIT", () => {
  // This test is very finnicky.
  // It has to return true || return false to reproduce. Throwing an error doesn't work.
  function run(start, prev) {
    while (true) {
      const current = performance.now();

      if (Number.isNaN(current) || current < prev) {
        return false;
      }

      if (current - start > 200) {
        return true;
      }
      prev = current;
    }
  }

  const start = performance.now();
  if (!run(start, start)) {
    throw new Error("performance.now() is not monotonic");
  }
});