Fake timers

Fake timers are synchronous implementations of setTimeout and friends that Sinon.JS can overwrite the global functions with to allow you to more easily test code using them. It also has utilities for working with async/Promise code.

Fake timers provide a clock object to pass time, which can also be used to control Date objects (e.g. new Date()) and the Temporal API (e.g. Temporal.Now.instant()).

For standalone usage of fake timers it is recommended to use fake-timers package instead. It provides the same set of features (Sinon uses it under the hood) and was previously extracted from Sinon.JS.

import t from "tap";
import sinon from "sinon";
import { JSDOM } from "jsdom";

t.test("fake timers can control time for animations and timeouts", (t) => {
  const dom = new JSDOM("<!DOCTYPE html><html><body></body></html>");
  const document = dom.window.document;

  const clock = sinon.useFakeTimers();

  // Create element and add to document
  const el = document.createElement("div");
  document.body.appendChild(el);

  // Animate function that changes styles over 500ms
  function animate(element) {
    setTimeout(() => {
      element.style.height = "200px";
      element.style.width = "200px";
    }, 500);
  }

  animate(el);

  // Verify animation hasn't completed yet
  t.equal(el.style.height, "", "height should be empty initially");
  t.equal(el.style.width, "", "width should be empty initially");

  // Advance time by 510ms
  clock.tick(510);

  // Verify animation completed
  t.equal(el.style.height, "200px", "height should be 200px after 510ms");
  t.equal(el.style.width, "200px", "width should be 200px after 510ms");

  clock.restore();
  t.end();
});

Fake timers ​

Fake timers