gecko-dev/browser/modules/test/head.js

Cu.import("resource://gre/modules/Promise.jsm");

const SINGLE_TRY_TIMEOUT = 100;
const NUMBER_OF_TRIES = 30;

function waitForConditionPromise(condition, timeoutMsg, tryCount=NUMBER_OF_TRIES) {
  let defer = Promise.defer();
  let tries = 0;
  function checkCondition() {
    if (tries >= tryCount) {
      defer.reject(timeoutMsg);
    }
    var conditionPassed;
    try {
      conditionPassed = condition();
    } catch (e) {
      return defer.reject(e);
    }
    if (conditionPassed) {
      return defer.resolve();
    }
    tries++;
    setTimeout(checkCondition, SINGLE_TRY_TIMEOUT);
  }
  setTimeout(checkCondition, SINGLE_TRY_TIMEOUT);
  return defer.promise;
}

function waitForCondition(condition, nextTest, errorMsg) {
  waitForConditionPromise(condition, errorMsg).then(nextTest, (reason) => {
    ok(false, reason + (reason.stack ? "\n" + e.stack : ""));
  });
}