docs/bundle.js
function shouldYield() {
    if (deadline === null) {
      return false;
    }
    if (deadline.timeRemaining() > timeHeuristicForUnitOfWork) {
      return false;
    }
    deadlineDidExpire = true;
    return true;
  }
function shouldYield() {
    if (deadline === null) {
      return false;
    }
    if (deadline.timeRemaining() > timeHeuristicForUnitOfWork) {
      return false;
    }
    deadlineDidExpire = true;
    return true;
  }
When working on async work, the reconciler asks the renderer if it should yield execution. For DOM, we implement this with requestIdleCallback.