Function useFiber

code/new-context-api/public/app.js:8328–8335

(fiber, pendingProps, expirationTime)

  }

  function useFiber(fiber, pendingProps, expirationTime) {
    // We currently set sibling to null and index to 0 here because it is easy
    // to forget to do before returning it. E.g. for the single child case.
    var clone = createWorkInProgress(fiber, pendingProps, expirationTime);
    clone.index = 0;
    clone.sibling = null;
    return clone;
  }

  function placeChild(newFiber, lastPlacedIndex, newIndex) {
    newFiber.index = newIndex;