EventPropagators.js

/**
 * Copyright 2013-2014 Facebook, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 * @providesModule EventPropagators
 */

"use strict";

var EventConstants = require('EventConstants');
var EventPluginHub = require('EventPluginHub');

var accumulate = require('accumulate');
var forEachAccumulated = require('forEachAccumulated');

var PropagationPhases = EventConstants.PropagationPhases;
var getListener = EventPluginHub.getListener;

/**
 * Some event types have a notion of different registration names for different
 * "phases" of propagation. This finds listeners by a given phase.
 */
function listenerAtPhase(id, event, propagationPhase) {
  var registrationName =
    event.dispatchConfig.phasedRegistrationNames[propagationPhase];
  return getListener(id, registrationName);
}

/**
 * Tags a `SyntheticEvent` with dispatched listeners. Creating this function
 * here, allows us to not have to bind or create functions for each event.
 * Mutating the event's members allows us to not have to create a wrapping
 * "dispatch" object that pairs the event with the listener.
 */
function accumulateDirectionalDispatches(domID, upwards, event) {
  if (__DEV__) {
    if (!domID) {
      throw new Error('Dispatching id must not be null');
    }
  }
  var phase = upwards ? PropagationPhases.bubbled : PropagationPhases.captured;
  var listener = listenerAtPhase(domID, event, phase);
  if (listener) {
    event._dispatchListeners = accumulate(event._dispatchListeners, listener);
    event._dispatchIDs = accumulate(event._dispatchIDs, domID);
  }
}

/**
 * Collect dispatches (must be entirely collected before dispatching - see unit
 * tests). Lazily allocate the array to conserve memory.  We must loop through
 * each event and perform the traversal for each one. We can not perform a
 * single traversal for the entire collection of events because each event may
 * have a different target.
 */
function accumulateTwoPhaseDispatchesSingle(event) {
  if (event && event.dispatchConfig.phasedRegistrationNames) {
    EventPluginHub.injection.getInstanceHandle().traverseTwoPhase(
      event.dispatchMarker,
      accumulateDirectionalDispatches,
      event
    );
  }
}


/**
 * Accumulates without regard to direction, does not look for phased
 * registration names. Same as `accumulateDirectDispatchesSingle` but without
 * requiring that the `dispatchMarker` be the same as the dispatched ID.
 */
function accumulateDispatches(id, ignoredDirection, event) {
  if (event && event.dispatchConfig.registrationName) {
    var registrationName = event.dispatchConfig.registrationName;
    var listener = getListener(id, registrationName);
    if (listener) {
      event._dispatchListeners = accumulate(event._dispatchListeners, listener);
      event._dispatchIDs = accumulate(event._dispatchIDs, id);
    }
  }
}

/**
 * Accumulates dispatches on an `SyntheticEvent`, but only for the
 * `dispatchMarker`.
 * @param {SyntheticEvent} event
 */
function accumulateDirectDispatchesSingle(event) {
  if (event && event.dispatchConfig.registrationName) {
    accumulateDispatches(event.dispatchMarker, null, event);
  }
}

function accumulateTwoPhaseDispatches(events) {
  forEachAccumulated(events, accumulateTwoPhaseDispatchesSingle);
}

function accumulateEnterLeaveDispatches(leave, enter, fromID, toID) {
  EventPluginHub.injection.getInstanceHandle().traverseEnterLeave(
    fromID,
    toID,
    accumulateDispatches,
    leave,
    enter
  );
}


function accumulateDirectDispatches(events) {
  forEachAccumulated(events, accumulateDirectDispatchesSingle);
}



/**
 * A small set of propagation patterns, each of which will accept a small amount
 * of information, and generate a set of "dispatch ready event objects" - which
 * are sets of events that have already been annotated with a set of dispatched
 * listener functions/ids. The API is designed this way to discourage these
 * propagation strategies from actually executing the dispatches, since we
 * always want to collect the entire set of dispatches before executing event a
 * single one.
 *
 * @constructor EventPropagators
 */
var EventPropagators = {
  accumulateTwoPhaseDispatches: accumulateTwoPhaseDispatches,
  accumulateDirectDispatches: accumulateDirectDispatches,
  accumulateEnterLeaveDispatches: accumulateEnterLeaveDispatches
};

module.exports = EventPropagators;