react/packages/events/ReactGenericBatching.js

/**
 * Copyright (c) Facebook, Inc. and its affiliates.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 */

import {
  needsStateRestore,
  restoreStateIfNeeded,
} from './ReactControlledComponent';
import {enableEventAPI} from 'shared/ReactFeatureFlags';

// Used as a way to call batchedUpdates when we don't have a reference to
// the renderer. Such as when we're dispatching events or if third party
// libraries need to call batchedUpdates. Eventually, this API will go away when
// everything is batched by default. We'll then have a similar API to opt-out of
// scheduled work and instead do synchronous work.

// Defaults
let batchedUpdatesImpl = function(fn, bookkeeping) {
  return fn(bookkeeping);
};
let discreteUpdatesImpl = function(fn, a, b, c) {
  return fn(a, b, c);
};
let flushDiscreteUpdatesImpl = function() {};
let batchedEventUpdatesImpl = batchedUpdatesImpl;

let isInsideEventHandler = false;

function finishEventHandler() {
  // Here we wait until all updates have propagated, which is important
  // when using controlled components within layers:
  // https://github.com/facebook/react/issues/1698
  // Then we restore state of any controlled component.
  const controlledComponentsHavePendingUpdates = needsStateRestore();
  if (controlledComponentsHavePendingUpdates) {
    // If a controlled event was fired, we may need to restore the state of
    // the DOM node back to the controlled value. This is necessary when React
    // bails out of the update without touching the DOM.
    flushDiscreteUpdatesImpl();
    restoreStateIfNeeded();
  }
}

export function batchedUpdates(fn, bookkeeping) {
  if (isInsideEventHandler) {
    // If we are currently inside another batch, we need to wait until it
    // fully completes before restoring state.
    return fn(bookkeeping);
  }
  isInsideEventHandler = true;
  try {
    return batchedUpdatesImpl(fn, bookkeeping);
  } finally {
    isInsideEventHandler = false;
    finishEventHandler();
  }
}

export function batchedEventUpdates(fn, bookkeeping) {
  if (isInsideEventHandler) {
    // If we are currently inside another batch, we need to wait until it
    // fully completes before restoring state.
    return fn(bookkeeping);
  }
  isInsideEventHandler = true;
  try {
    return batchedEventUpdatesImpl(fn, bookkeeping);
  } finally {
    isInsideEventHandler = false;
    finishEventHandler();
  }
}

export function discreteUpdates(fn, a, b, c) {
  const prevIsInsideEventHandler = isInsideEventHandler;
  isInsideEventHandler = true;
  try {
    return discreteUpdatesImpl(fn, a, b, c);
  } finally {
    isInsideEventHandler = prevIsInsideEventHandler;
    if (!isInsideEventHandler) {
      finishEventHandler();
    }
  }
}

let lastFlushedEventTimeStamp = 0;
export function flushDiscreteUpdatesIfNeeded(timeStamp: number) {
  // event.timeStamp isn't overly reliable due to inconsistencies in
  // how different browsers have historically provided the time stamp.
  // Some browsers provide high-resolution time stamps for all events,
  // some provide low-resoltion time stamps for all events. FF < 52
  // even mixes both time stamps together. Some browsers even report
  // negative time stamps or time stamps that are 0 (iOS9) in some cases.
  // Given we are only comparing two time stamps with equality (!==),
  // we are safe from the resolution differences. If the time stamp is 0
  // we bail-out of preventing the flush, which can affect semantics,
  // such as if an earlier flush removes or adds event listeners that
  // are fired in the subsequent flush. However, this is the same
  // behaviour as we had before this change, so the risks are low.
  if (
    !isInsideEventHandler &&
    (!enableEventAPI ||
      (timeStamp === 0 || lastFlushedEventTimeStamp !== timeStamp))
  ) {
    lastFlushedEventTimeStamp = timeStamp;
    flushDiscreteUpdatesImpl();
  }
}

export function setBatchingImplementation(
  _batchedUpdatesImpl,
  _discreteUpdatesImpl,
  _flushDiscreteUpdatesImpl,
  _batchedEventUpdatesImpl,
) {
  batchedUpdatesImpl = _batchedUpdatesImpl;
  discreteUpdatesImpl = _discreteUpdatesImpl;
  flushDiscreteUpdatesImpl = _flushDiscreteUpdatesImpl;
  batchedEventUpdatesImpl = _batchedEventUpdatesImpl;
}