Useful promisified timeout with cancellation

timeout.js

module.exports.timeout = function timeout(ms, clear = () => {}) {
  return new Promise((res, rej) => {
    var t = setTimeout(res, ms);
    clear(function cancel () {
      clearTimeout(t);
      rej("CANCELLED BY TIMEOUT");
    });
  });
};

timeout_test.js

var { timeout } = require("./timeout");

// scenario 1: regular timeout
(async () => {
  await timeout(1000);
  console.log("scenario 1 done");
})();

// scenario 2: cancellation
(async () => {
  let passed = true;
  try {
    await timeout(1000, async function(cancel) {
      await timeout(500);
      cancel();
    });
    passed = false;
  } catch (err) {
    // ignore error
  }
  if (passed) {
    console.log("scenario 2 passed");
  } else {
    console.log("scenario 2 failed");
  }
})();