React中Transition的作用

/**
 * `Transaction` creates a black box that is able to wrap any method such that
 * certain invariants are maintained before and after the method is invoked
 * (Even if an exception is thrown while invoking the wrapped method). Whoever
 * instantiates a transaction can provide enforcers of the invariants at
 * creation time. The `Transaction` class itself will supply one additional
 * automatic invariant for you - the invariant that any transaction instance
 * should not be run while it is already being run. You would typically create a
 * single instance of a `Transaction` for reuse multiple times, that potentially
 * is used to wrap several different methods. Wrappers are extremely simple -
 * they only require implementing two methods.
 *
 * <pre>
 *                       wrappers (injected at creation time)
 *                                      +        +
 *                                      |        |
 *                    +-----------------|--------|--------------+
 *                    |                 v        |              |
 *                    |      +---------------+   |              |
 *                    |   +--|    wrapper1   |---|----+         |
 *                    |   |  +---------------+   v    |         |
 *                    |   |          +-------------+  |         |
 *                    |   |     +----|   wrapper2  |--------+   |
 *                    |   |     |    +-------------+  |     |   |
 *                    |   |     |                     |     |   |
 *                    |   v     v                     v     v   | wrapper
 *                    | +---+ +---+   +---------+   +---+ +---+ | invariants
 * perform(anyMethod) | |   | |   |   |         |   |   | |   | | maintained
 * +----------------->|-|---|-|---|-->|anyMethod|---|---|-|---|-|-------->
 *                    | |   | |   |   |         |   |   | |   | |
 *                    | |   | |   |   |         |   |   | |   | |
 *                    | |   | |   |   |         |   |   | |   | |
 *                    | +---+ +---+   +---------+   +---+ +---+ |
 *                    |  initialize                    close    |
 *                    +-----------------------------------------+
 * </pre>
 *
 * Use cases:
 * - Preserving the input selection ranges before/after reconciliation.
 *   Restoring selection even in the event of an unexpected error.
 * - Deactivating events while rearranging the DOM, preventing blurs/focuses,
 *   while guaranteeing that afterwards, the event system is reactivated.
 * - Flushing a queue of collected DOM mutations to the main UI thread after a
 *   reconciliation takes place in a worker thread.
 * - Invoking any collected `componentDidUpdate` callbacks after rendering new
 *   content.
 * - (Future use case): Wrapping particular flushes of the `ReactWorker` queue
 *   to preserve the `scrollTop` (an automatic scroll aware DOM).
 * - (Future use case): Layout calculations before and after DOM updates.
 *
 * Transactional plugin API:
 * - A module that has an `initialize` method that returns any precomputation.
 * - and a `close` method that accepts the precomputation. `close` is invoked
 *   when the wrapped process is completed, or has failed.
 *
 * @param {Array<TransactionalWrapper>} transactionWrapper Wrapper modules
 * that implement `initialize` and `close`.
 * @return {Transaction} Single transaction for reuse in thread.
 *
 * @class Transaction
 */

简单的说就是，加入到某个transaction中之后，这个transaction会有前置和后置的wrapper，不如停止event，还原selection之类的。