EventPropagators.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 {
  getParentInstance,
  traverseTwoPhase,
  traverseEnterLeave,
} from 'shared/ReactTreeTraversal';
import warning from 'shared/warning';

import {getListener} from './EventPluginHub';
import accumulateInto from './accumulateInto';
import forEachAccumulated from './forEachAccumulated';

type PropagationPhases = 'bubbled' | 'captured';

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

/**
 * 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 even a
 * single one.
 */

/**
 * 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(inst, phase, event) {
  if (__DEV__) {
    if (!inst) {
      warning('Dispatching inst must not be null');
    }
  }
  const listener = listenerAtPhase(inst, event, phase);
  if (listener) {
    event._dispatchListeners = accumulateInto(
      event._dispatchListeners,
      listener,
    );
    event._dispatchInstances = accumulateInto(event._dispatchInstances, inst);
  }
}

/**
 * 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 cannot 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) {
    traverseTwoPhase(event._targetInst, accumulateDirectionalDispatches, event);
  }
}

/**
 * Same as `accumulateTwoPhaseDispatchesSingle`, but skips over the targetID.
 */
function accumulateTwoPhaseDispatchesSingleSkipTarget(event) {
  if (event && event.dispatchConfig.phasedRegistrationNames) {
    const targetInst = event._targetInst;
    const parentInst = targetInst ? getParentInstance(targetInst) : null;
    traverseTwoPhase(parentInst, 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(inst, ignoredDirection, event) {
  if (inst && event && event.dispatchConfig.registrationName) {
    const registrationName = event.dispatchConfig.registrationName;
    const listener = getListener(inst, registrationName);
    if (listener) {
      event._dispatchListeners = accumulateInto(
        event._dispatchListeners,
        listener,
      );
      event._dispatchInstances = accumulateInto(event._dispatchInstances, inst);
    }
  }
}

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

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

export function accumulateTwoPhaseDispatchesSkipTarget(events) {
  forEachAccumulated(events, accumulateTwoPhaseDispatchesSingleSkipTarget);
}

export function accumulateEnterLeaveDispatches(leave, enter, from, to) {
  traverseEnterLeave(from, to, accumulateDispatches, leave, enter);
}

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