diff --git a/packages/events/EventPluginHub.js b/packages/events/EventPluginHub.js
index 7da9a5ea7a..48d7d6bc51 100644
--- a/packages/events/EventPluginHub.js
+++ b/packages/events/EventPluginHub.js
@@ -30,7 +30,7 @@ import type {AnyNativeEvent} from './PluginModuleType';
  * Internal queue of events that have accumulated their dispatches and are
  * waiting to have their dispatches executed.
  */
-var eventQueue: ?(Array<ReactSyntheticEvent> | ReactSyntheticEvent) = null;
+let eventQueue: ?(Array<ReactSyntheticEvent> | ReactSyntheticEvent) = null;
 
 /**
  * Dispatches an event and releases it back into the pool, unless persistent.
@@ -39,7 +39,7 @@ var eventQueue: ?(Array<ReactSyntheticEvent> | ReactSyntheticEvent) = null;
  * @param {boolean} simulated If the event is simulated (changes exn behavior)
  * @private
  */
-var executeDispatchesAndRelease = function(
+const executeDispatchesAndRelease = function(
   event: ReactSyntheticEvent,
   simulated: boolean,
 ) {
@@ -51,10 +51,10 @@ var executeDispatchesAndRelease = function(
     }
   }
 };
-var executeDispatchesAndReleaseSimulated = function(e) {
+const executeDispatchesAndReleaseSimulated = function(e) {
   return executeDispatchesAndRelease(e, true);
 };
-var executeDispatchesAndReleaseTopLevel = function(e) {
+const executeDispatchesAndReleaseTopLevel = function(e) {
   return executeDispatchesAndRelease(e, false);
 };
 
@@ -130,7 +130,7 @@ export const injection = {
  * @return {?function} The stored callback.
  */
 export function getListener(inst: Fiber, registrationName: string) {
-  var listener;
+  let listener;
 
   // TODO: shouldPreventMouseEvent is DOM-specific and definitely should not
   // live here; needs to be moved to a better place soon
@@ -170,12 +170,12 @@ export function extractEvents(
   nativeEvent: AnyNativeEvent,
   nativeEventTarget: EventTarget,
 ) {
-  var events;
-  for (var i = 0; i < plugins.length; i++) {
+  let events;
+  for (let i = 0; i < plugins.length; i++) {
     // Not every plugin in the ordering may be loaded at runtime.
-    var possiblePlugin: PluginModule<AnyNativeEvent> = plugins[i];
+    const possiblePlugin: PluginModule<AnyNativeEvent> = plugins[i];
     if (possiblePlugin) {
-      var extractedEvents = possiblePlugin.extractEvents(
+      const extractedEvents = possiblePlugin.extractEvents(
         topLevelType,
         targetInst,
         nativeEvent,
@@ -212,7 +212,7 @@ export function enqueueEvents(
 export function processEventQueue(simulated: boolean) {
   // Set `eventQueue` to null before processing it so that we can tell if more
   // events get enqueued while processing.
-  var processingEventQueue = eventQueue;
+  const processingEventQueue = eventQueue;
   eventQueue = null;
 
   if (!processingEventQueue) {
diff --git a/packages/events/EventPluginRegistry.js b/packages/events/EventPluginRegistry.js
index ebd527ebc1..ccfaa872dc 100644
--- a/packages/events/EventPluginRegistry.js
+++ b/packages/events/EventPluginRegistry.js
@@ -20,17 +20,17 @@ import lowPriorityWarning from 'shared/lowPriorityWarning';
 type NamesToPlugins = {[key: PluginName]: PluginModule<AnyNativeEvent>};
 type EventPluginOrder = null | Array<PluginName>;
 
-var shouldWarnOnInjection = false;
+let shouldWarnOnInjection = false;
 
 /**
  * Injectable ordering of event plugins.
  */
-var eventPluginOrder: EventPluginOrder = null;
+let eventPluginOrder: EventPluginOrder = null;
 
 /**
  * Injectable mapping from names to event plugin modules.
  */
-var namesToPlugins: NamesToPlugins = {};
+const namesToPlugins: NamesToPlugins = {};
 
 export function enableWarningOnInjection() {
   shouldWarnOnInjection = true;
@@ -46,9 +46,9 @@ function recomputePluginOrdering(): void {
     // Wait until an `eventPluginOrder` is injected.
     return;
   }
-  for (var pluginName in namesToPlugins) {
-    var pluginModule = namesToPlugins[pluginName];
-    var pluginIndex = eventPluginOrder.indexOf(pluginName);
+  for (const pluginName in namesToPlugins) {
+    const pluginModule = namesToPlugins[pluginName];
+    const pluginIndex = eventPluginOrder.indexOf(pluginName);
     invariant(
       pluginIndex > -1,
       'EventPluginRegistry: Cannot inject event plugins that do not exist in ' +
@@ -65,8 +65,8 @@ function recomputePluginOrdering(): void {
       pluginName,
     );
     plugins[pluginIndex] = pluginModule;
-    var publishedEvents = pluginModule.eventTypes;
-    for (var eventName in publishedEvents) {
+    const publishedEvents = pluginModule.eventTypes;
+    for (const eventName in publishedEvents) {
       invariant(
         publishEventForPlugin(
           publishedEvents[eventName],
@@ -102,11 +102,11 @@ function publishEventForPlugin(
   );
   eventNameDispatchConfigs[eventName] = dispatchConfig;
 
-  var phasedRegistrationNames = dispatchConfig.phasedRegistrationNames;
+  const phasedRegistrationNames = dispatchConfig.phasedRegistrationNames;
   if (phasedRegistrationNames) {
-    for (var phaseName in phasedRegistrationNames) {
+    for (const phaseName in phasedRegistrationNames) {
       if (phasedRegistrationNames.hasOwnProperty(phaseName)) {
-        var phasedRegistrationName = phasedRegistrationNames[phaseName];
+        const phasedRegistrationName = phasedRegistrationNames[phaseName];
         publishRegistrationName(
           phasedRegistrationName,
           pluginModule,
@@ -149,7 +149,7 @@ function publishRegistrationName(
     pluginModule.eventTypes[eventName].dependencies;
 
   if (__DEV__) {
-    var lowerCasedName = registrationName.toLowerCase();
+    const lowerCasedName = registrationName.toLowerCase();
     possibleRegistrationNames[lowerCasedName] = registrationName;
 
     if (registrationName === 'onDoubleClick') {
@@ -243,12 +243,12 @@ export function injectEventPluginsByName(
     }
   }
 
-  var isOrderingDirty = false;
-  for (var pluginName in injectedNamesToPlugins) {
+  let isOrderingDirty = false;
+  for (const pluginName in injectedNamesToPlugins) {
     if (!injectedNamesToPlugins.hasOwnProperty(pluginName)) {
       continue;
     }
-    var pluginModule = injectedNamesToPlugins[pluginName];
+    const pluginModule = injectedNamesToPlugins[pluginName];
     if (
       !namesToPlugins.hasOwnProperty(pluginName) ||
       namesToPlugins[pluginName] !== pluginModule
diff --git a/packages/events/EventPluginUtils.js b/packages/events/EventPluginUtils.js
index 12e71021c9..d5e5a5e847 100644
--- a/packages/events/EventPluginUtils.js
+++ b/packages/events/EventPluginUtils.js
@@ -45,19 +45,19 @@ export function isStartish(topLevelType) {
   return topLevelType === 'topMouseDown' || topLevelType === 'topTouchStart';
 }
 
-var validateEventDispatches;
+let validateEventDispatches;
 if (__DEV__) {
   validateEventDispatches = function(event) {
-    var dispatchListeners = event._dispatchListeners;
-    var dispatchInstances = event._dispatchInstances;
+    const dispatchListeners = event._dispatchListeners;
+    const dispatchInstances = event._dispatchInstances;
 
-    var listenersIsArr = Array.isArray(dispatchListeners);
-    var listenersLen = listenersIsArr
+    const listenersIsArr = Array.isArray(dispatchListeners);
+    const listenersLen = listenersIsArr
       ? dispatchListeners.length
       : dispatchListeners ? 1 : 0;
 
-    var instancesIsArr = Array.isArray(dispatchInstances);
-    var instancesLen = instancesIsArr
+    const instancesIsArr = Array.isArray(dispatchInstances);
+    const instancesLen = instancesIsArr
       ? dispatchInstances.length
       : dispatchInstances ? 1 : 0;
 
@@ -76,7 +76,7 @@ if (__DEV__) {
  * @param {*} inst Internal component instance
  */
 function executeDispatch(event, simulated, listener, inst) {
-  var type = event.type || 'unknown-event';
+  const type = event.type || 'unknown-event';
   event.currentTarget = getNodeFromInstance(inst);
   ReactErrorUtils.invokeGuardedCallbackAndCatchFirstError(
     type,
@@ -91,13 +91,13 @@ function executeDispatch(event, simulated, listener, inst) {
  * Standard/simple iteration through an event's collected dispatches.
  */
 export function executeDispatchesInOrder(event, simulated) {
-  var dispatchListeners = event._dispatchListeners;
-  var dispatchInstances = event._dispatchInstances;
+  const dispatchListeners = event._dispatchListeners;
+  const dispatchInstances = event._dispatchInstances;
   if (__DEV__) {
     validateEventDispatches(event);
   }
   if (Array.isArray(dispatchListeners)) {
-    for (var i = 0; i < dispatchListeners.length; i++) {
+    for (let i = 0; i < dispatchListeners.length; i++) {
       if (event.isPropagationStopped()) {
         break;
       }
@@ -124,13 +124,13 @@ export function executeDispatchesInOrder(event, simulated) {
  * true, or null if no listener returned true.
  */
 function executeDispatchesInOrderStopAtTrueImpl(event) {
-  var dispatchListeners = event._dispatchListeners;
-  var dispatchInstances = event._dispatchInstances;
+  const dispatchListeners = event._dispatchListeners;
+  const dispatchInstances = event._dispatchInstances;
   if (__DEV__) {
     validateEventDispatches(event);
   }
   if (Array.isArray(dispatchListeners)) {
-    for (var i = 0; i < dispatchListeners.length; i++) {
+    for (let i = 0; i < dispatchListeners.length; i++) {
       if (event.isPropagationStopped()) {
         break;
       }
@@ -151,7 +151,7 @@ function executeDispatchesInOrderStopAtTrueImpl(event) {
  * @see executeDispatchesInOrderStopAtTrueImpl
  */
 export function executeDispatchesInOrderStopAtTrue(event) {
-  var ret = executeDispatchesInOrderStopAtTrueImpl(event);
+  const ret = executeDispatchesInOrderStopAtTrueImpl(event);
   event._dispatchInstances = null;
   event._dispatchListeners = null;
   return ret;
@@ -170,8 +170,8 @@ export function executeDirectDispatch(event) {
   if (__DEV__) {
     validateEventDispatches(event);
   }
-  var dispatchListener = event._dispatchListeners;
-  var dispatchInstance = event._dispatchInstances;
+  const dispatchListener = event._dispatchListeners;
+  const dispatchInstance = event._dispatchInstances;
   invariant(
     !Array.isArray(dispatchListener),
     'executeDirectDispatch(...): Invalid `event`.',
@@ -179,7 +179,7 @@ export function executeDirectDispatch(event) {
   event.currentTarget = dispatchListener
     ? getNodeFromInstance(dispatchInstance)
     : null;
-  var res = dispatchListener ? dispatchListener(event) : null;
+  const res = dispatchListener ? dispatchListener(event) : null;
   event.currentTarget = null;
   event._dispatchListeners = null;
   event._dispatchInstances = null;
diff --git a/packages/events/EventPropagators.js b/packages/events/EventPropagators.js
index f54440e3d3..451d18b852 100644
--- a/packages/events/EventPropagators.js
+++ b/packages/events/EventPropagators.js
@@ -23,7 +23,7 @@ type PropagationPhases = 'bubbled' | 'captured';
  * "phases" of propagation. This finds listeners by a given phase.
  */
 function listenerAtPhase(inst, event, propagationPhase: PropagationPhases) {
-  var registrationName =
+  const registrationName =
     event.dispatchConfig.phasedRegistrationNames[propagationPhase];
   return getListener(inst, registrationName);
 }
@@ -48,7 +48,7 @@ function accumulateDirectionalDispatches(inst, phase, event) {
   if (__DEV__) {
     warning(inst, 'Dispatching inst must not be null');
   }
-  var listener = listenerAtPhase(inst, event, phase);
+  const listener = listenerAtPhase(inst, event, phase);
   if (listener) {
     event._dispatchListeners = accumulateInto(
       event._dispatchListeners,
@@ -76,8 +76,8 @@ function accumulateTwoPhaseDispatchesSingle(event) {
  */
 function accumulateTwoPhaseDispatchesSingleSkipTarget(event) {
   if (event && event.dispatchConfig.phasedRegistrationNames) {
-    var targetInst = event._targetInst;
-    var parentInst = targetInst ? getParentInstance(targetInst) : null;
+    const targetInst = event._targetInst;
+    const parentInst = targetInst ? getParentInstance(targetInst) : null;
     traverseTwoPhase(parentInst, accumulateDirectionalDispatches, event);
   }
 }
@@ -89,8 +89,8 @@ function accumulateTwoPhaseDispatchesSingleSkipTarget(event) {
  */
 function accumulateDispatches(inst, ignoredDirection, event) {
   if (inst && event && event.dispatchConfig.registrationName) {
-    var registrationName = event.dispatchConfig.registrationName;
-    var listener = getListener(inst, registrationName);
+    const registrationName = event.dispatchConfig.registrationName;
+    const listener = getListener(inst, registrationName);
     if (listener) {
       event._dispatchListeners = accumulateInto(
         event._dispatchListeners,
diff --git a/packages/events/ReactControlledComponent.js b/packages/events/ReactControlledComponent.js
index 59a7b623e3..c03233cc21 100644
--- a/packages/events/ReactControlledComponent.js
+++ b/packages/events/ReactControlledComponent.js
@@ -14,9 +14,9 @@ import {
 
 // Use to restore controlled state after a change event has fired.
 
-var fiberHostComponent = null;
+let fiberHostComponent = null;
 
-var ReactControlledComponentInjection = {
+const ReactControlledComponentInjection = {
   injectFiberControlledHostComponent: function(hostComponentImpl) {
     // The fiber implementation doesn't use dynamic dispatch so we need to
     // inject the implementation.
@@ -24,13 +24,13 @@ var ReactControlledComponentInjection = {
   },
 };
 
-var restoreTarget = null;
-var restoreQueue = null;
+let restoreTarget = null;
+let restoreQueue = null;
 
 function restoreStateOfTarget(target) {
   // We perform this translation at the end of the event loop so that we
   // always receive the correct fiber here
-  var internalInstance = getInstanceFromNode(target);
+  const internalInstance = getInstanceFromNode(target);
   if (!internalInstance) {
     // Unmounted
     return;
@@ -67,14 +67,14 @@ export function restoreStateIfNeeded() {
   if (!restoreTarget) {
     return;
   }
-  var target = restoreTarget;
-  var queuedTargets = restoreQueue;
+  const target = restoreTarget;
+  const queuedTargets = restoreQueue;
   restoreTarget = null;
   restoreQueue = null;
 
   restoreStateOfTarget(target);
   if (queuedTargets) {
-    for (var i = 0; i < queuedTargets.length; i++) {
+    for (let i = 0; i < queuedTargets.length; i++) {
       restoreStateOfTarget(queuedTargets[i]);
     }
   }
diff --git a/packages/events/ReactEventEmitterMixin.js b/packages/events/ReactEventEmitterMixin.js
index 43b0e6eca2..86bfe2e761 100644
--- a/packages/events/ReactEventEmitterMixin.js
+++ b/packages/events/ReactEventEmitterMixin.js
@@ -26,7 +26,7 @@ export function handleTopLevel(
   nativeEvent,
   nativeEventTarget,
 ) {
-  var events = extractEvents(
+  const events = extractEvents(
     topLevelType,
     targetInst,
     nativeEvent,
diff --git a/packages/events/ReactGenericBatching.js b/packages/events/ReactGenericBatching.js
index 42b27fd473..3e22cd54ce 100644
--- a/packages/events/ReactGenericBatching.js
+++ b/packages/events/ReactGenericBatching.js
@@ -14,11 +14,11 @@ import {restoreStateIfNeeded} from './ReactControlledComponent';
 // scheduled work and instead do synchronous work.
 
 // Defaults
-var fiberBatchedUpdates = function(fn, bookkeeping) {
+let fiberBatchedUpdates = function(fn, bookkeeping) {
   return fn(bookkeeping);
 };
 
-var isNestingBatched = false;
+let isNestingBatched = false;
 export function batchedUpdates(fn, bookkeeping) {
   if (isNestingBatched) {
     // If we are currently inside another batch, we need to wait until it
@@ -39,7 +39,7 @@ export function batchedUpdates(fn, bookkeeping) {
   }
 }
 
-var ReactGenericBatchingInjection = {
+const ReactGenericBatchingInjection = {
   injectFiberBatchedUpdates: function(_batchedUpdates) {
     fiberBatchedUpdates = _batchedUpdates;
   },
diff --git a/packages/events/ResponderEventPlugin.js b/packages/events/ResponderEventPlugin.js
index c2d599bcca..202f8931f9 100644
--- a/packages/events/ResponderEventPlugin.js
+++ b/packages/events/ResponderEventPlugin.js
@@ -29,21 +29,21 @@ import accumulate from './accumulate';
  * Instance of element that should respond to touch/move types of interactions,
  * as indicated explicitly by relevant callbacks.
  */
-var responderInst = null;
+let responderInst = null;
 
 /**
  * Count of current touches. A textInput should become responder iff the
  * selection changes while there is a touch on the screen.
  */
-var trackedTouchCount = 0;
+let trackedTouchCount = 0;
 
 /**
  * Last reported number of active touches.
  */
-var previousActiveTouches = 0;
+let previousActiveTouches = 0;
 
-var changeResponder = function(nextResponderInst, blockHostResponder) {
-  var oldResponderInst = responderInst;
+const changeResponder = function(nextResponderInst, blockHostResponder) {
+  const oldResponderInst = responderInst;
   responderInst = nextResponderInst;
   if (ResponderEventPlugin.GlobalResponderHandler !== null) {
     ResponderEventPlugin.GlobalResponderHandler.onChange(
@@ -54,7 +54,7 @@ var changeResponder = function(nextResponderInst, blockHostResponder) {
   }
 };
 
-var eventTypes = {
+const eventTypes = {
   /**
    * On a `touchStart`/`mouseDown`, is it desired that this element become the
    * responder?
@@ -318,7 +318,7 @@ function setResponderAndExtractTransfer(
   nativeEvent,
   nativeEventTarget,
 ) {
-  var shouldSetEventType = isStartish(topLevelType)
+  const shouldSetEventType = isStartish(topLevelType)
     ? eventTypes.startShouldSetResponder
     : isMoveish(topLevelType)
       ? eventTypes.moveShouldSetResponder
@@ -327,7 +327,7 @@ function setResponderAndExtractTransfer(
         : eventTypes.scrollShouldSetResponder;
 
   // TODO: stop one short of the current responder.
-  var bubbleShouldSetFrom = !responderInst
+  const bubbleShouldSetFrom = !responderInst
     ? targetInst
     : getLowestCommonAncestor(responderInst, targetInst);
 
@@ -335,8 +335,8 @@ function setResponderAndExtractTransfer(
   // (deepest ID) if it happens to be the current responder. The reasoning:
   // It's strange to get an `onMoveShouldSetResponder` when you're *already*
   // the responder.
-  var skipOverBubbleShouldSetFrom = bubbleShouldSetFrom === responderInst;
-  var shouldSetEvent = ResponderSyntheticEvent.getPooled(
+  const skipOverBubbleShouldSetFrom = bubbleShouldSetFrom === responderInst;
+  const shouldSetEvent = ResponderSyntheticEvent.getPooled(
     shouldSetEventType,
     bubbleShouldSetFrom,
     nativeEvent,
@@ -348,7 +348,7 @@ function setResponderAndExtractTransfer(
   } else {
     accumulateTwoPhaseDispatches(shouldSetEvent);
   }
-  var wantsResponderInst = executeDispatchesInOrderStopAtTrue(shouldSetEvent);
+  const wantsResponderInst = executeDispatchesInOrderStopAtTrue(shouldSetEvent);
   if (!shouldSetEvent.isPersistent()) {
     shouldSetEvent.constructor.release(shouldSetEvent);
   }
@@ -356,8 +356,8 @@ function setResponderAndExtractTransfer(
   if (!wantsResponderInst || wantsResponderInst === responderInst) {
     return null;
   }
-  var extracted;
-  var grantEvent = ResponderSyntheticEvent.getPooled(
+  let extracted;
+  const grantEvent = ResponderSyntheticEvent.getPooled(
     eventTypes.responderGrant,
     wantsResponderInst,
     nativeEvent,
@@ -366,9 +366,9 @@ function setResponderAndExtractTransfer(
   grantEvent.touchHistory = ResponderTouchHistoryStore.touchHistory;
 
   accumulateDirectDispatches(grantEvent);
-  var blockHostResponder = executeDirectDispatch(grantEvent) === true;
+  const blockHostResponder = executeDirectDispatch(grantEvent) === true;
   if (responderInst) {
-    var terminationRequestEvent = ResponderSyntheticEvent.getPooled(
+    const terminationRequestEvent = ResponderSyntheticEvent.getPooled(
       eventTypes.responderTerminationRequest,
       responderInst,
       nativeEvent,
@@ -377,7 +377,7 @@ function setResponderAndExtractTransfer(
     terminationRequestEvent.touchHistory =
       ResponderTouchHistoryStore.touchHistory;
     accumulateDirectDispatches(terminationRequestEvent);
-    var shouldSwitch =
+    const shouldSwitch =
       !hasDispatches(terminationRequestEvent) ||
       executeDirectDispatch(terminationRequestEvent);
     if (!terminationRequestEvent.isPersistent()) {
@@ -385,7 +385,7 @@ function setResponderAndExtractTransfer(
     }
 
     if (shouldSwitch) {
-      var terminateEvent = ResponderSyntheticEvent.getPooled(
+      const terminateEvent = ResponderSyntheticEvent.getPooled(
         eventTypes.responderTerminate,
         responderInst,
         nativeEvent,
@@ -396,7 +396,7 @@ function setResponderAndExtractTransfer(
       extracted = accumulate(extracted, [grantEvent, terminateEvent]);
       changeResponder(wantsResponderInst, blockHostResponder);
     } else {
-      var rejectEvent = ResponderSyntheticEvent.getPooled(
+      const rejectEvent = ResponderSyntheticEvent.getPooled(
         eventTypes.responderReject,
         wantsResponderInst,
         nativeEvent,
@@ -442,16 +442,16 @@ function canTriggerTransfer(topLevelType, topLevelInst, nativeEvent) {
  * @return {boolean} Whether or not this touch end event ends the responder.
  */
 function noResponderTouches(nativeEvent) {
-  var touches = nativeEvent.touches;
+  const touches = nativeEvent.touches;
   if (!touches || touches.length === 0) {
     return true;
   }
-  for (var i = 0; i < touches.length; i++) {
-    var activeTouch = touches[i];
-    var target = activeTouch.target;
+  for (let i = 0; i < touches.length; i++) {
+    const activeTouch = touches[i];
+    const target = activeTouch.target;
     if (target !== null && target !== undefined && target !== 0) {
       // Is the original touch location inside of the current responder?
-      var targetInst = getInstanceFromNode(target);
+      const targetInst = getInstanceFromNode(target);
       if (isAncestor(responderInst, targetInst)) {
         return false;
       }
@@ -460,7 +460,7 @@ function noResponderTouches(nativeEvent) {
   return true;
 }
 
-var ResponderEventPlugin = {
+const ResponderEventPlugin = {
   /* For unit testing only */
   _getResponder: function() {
     return responderInst;
@@ -494,7 +494,7 @@ var ResponderEventPlugin = {
 
     ResponderTouchHistoryStore.recordTouchTrack(topLevelType, nativeEvent);
 
-    var extracted = canTriggerTransfer(topLevelType, targetInst, nativeEvent)
+    let extracted = canTriggerTransfer(topLevelType, targetInst, nativeEvent)
       ? setResponderAndExtractTransfer(
           topLevelType,
           targetInst,
@@ -512,17 +512,17 @@ var ResponderEventPlugin = {
     // These multiple individual change touch events are are always bookended
     // by `onResponderGrant`, and one of
     // (`onResponderRelease/onResponderTerminate`).
-    var isResponderTouchStart = responderInst && isStartish(topLevelType);
-    var isResponderTouchMove = responderInst && isMoveish(topLevelType);
-    var isResponderTouchEnd = responderInst && isEndish(topLevelType);
-    var incrementalTouch = isResponderTouchStart
+    const isResponderTouchStart = responderInst && isStartish(topLevelType);
+    const isResponderTouchMove = responderInst && isMoveish(topLevelType);
+    const isResponderTouchEnd = responderInst && isEndish(topLevelType);
+    const incrementalTouch = isResponderTouchStart
       ? eventTypes.responderStart
       : isResponderTouchMove
         ? eventTypes.responderMove
         : isResponderTouchEnd ? eventTypes.responderEnd : null;
 
     if (incrementalTouch) {
-      var gesture = ResponderSyntheticEvent.getPooled(
+      const gesture = ResponderSyntheticEvent.getPooled(
         incrementalTouch,
         responderInst,
         nativeEvent,
@@ -533,18 +533,18 @@ var ResponderEventPlugin = {
       extracted = accumulate(extracted, gesture);
     }
 
-    var isResponderTerminate =
+    const isResponderTerminate =
       responderInst && topLevelType === 'topTouchCancel';
-    var isResponderRelease =
+    const isResponderRelease =
       responderInst &&
       !isResponderTerminate &&
       isEndish(topLevelType) &&
       noResponderTouches(nativeEvent);
-    var finalTouch = isResponderTerminate
+    const finalTouch = isResponderTerminate
       ? eventTypes.responderTerminate
       : isResponderRelease ? eventTypes.responderRelease : null;
     if (finalTouch) {
-      var finalEvent = ResponderSyntheticEvent.getPooled(
+      const finalEvent = ResponderSyntheticEvent.getPooled(
         finalTouch,
         responderInst,
         nativeEvent,
@@ -556,7 +556,7 @@ var ResponderEventPlugin = {
       changeResponder(null);
     }
 
-    var numberActiveTouches =
+    const numberActiveTouches =
       ResponderTouchHistoryStore.touchHistory.numberActiveTouches;
     if (
       ResponderEventPlugin.GlobalInteractionHandler &&
diff --git a/packages/events/ResponderSyntheticEvent.js b/packages/events/ResponderSyntheticEvent.js
index 8f94680fdb..74ab4003a0 100644
--- a/packages/events/ResponderSyntheticEvent.js
+++ b/packages/events/ResponderSyntheticEvent.js
@@ -12,7 +12,7 @@ import SyntheticEvent from './SyntheticEvent';
  * interface will ensure that it is cleaned up when pooled/destroyed. The
  * `ResponderEventPlugin` will populate it appropriately.
  */
-var ResponderEventInterface = {
+const ResponderEventInterface = {
   touchHistory: function(nativeEvent) {
     return null; // Actually doesn't even look at the native event.
   },
diff --git a/packages/events/SyntheticEvent.js b/packages/events/SyntheticEvent.js
index d3dfd7ab72..1fb66f6e46 100644
--- a/packages/events/SyntheticEvent.js
+++ b/packages/events/SyntheticEvent.js
@@ -11,11 +11,11 @@ import emptyFunction from 'fbjs/lib/emptyFunction';
 import invariant from 'fbjs/lib/invariant';
 import warning from 'fbjs/lib/warning';
 
-var didWarnForAddedNewProperty = false;
-var isProxySupported = typeof Proxy === 'function';
-var EVENT_POOL_SIZE = 10;
+let didWarnForAddedNewProperty = false;
+const isProxySupported = typeof Proxy === 'function';
+const EVENT_POOL_SIZE = 10;
 
-var shouldBeReleasedProperties = [
+const shouldBeReleasedProperties = [
   'dispatchConfig',
   '_targetInst',
   'nativeEvent',
@@ -29,7 +29,7 @@ var shouldBeReleasedProperties = [
  * @interface Event
  * @see http://www.w3.org/TR/DOM-Level-3-Events/
  */
-var EventInterface = {
+const EventInterface = {
   type: null,
   target: null,
   // currentTarget is set when dispatching; no use in copying it here
@@ -79,15 +79,15 @@ function SyntheticEvent(
   this._targetInst = targetInst;
   this.nativeEvent = nativeEvent;
 
-  var Interface = this.constructor.Interface;
-  for (var propName in Interface) {
+  const Interface = this.constructor.Interface;
+  for (const propName in Interface) {
     if (!Interface.hasOwnProperty(propName)) {
       continue;
     }
     if (__DEV__) {
       delete this[propName]; // this has a getter/setter for warnings
     }
-    var normalize = Interface[propName];
+    const normalize = Interface[propName];
     if (normalize) {
       this[propName] = normalize(nativeEvent);
     } else {
@@ -99,7 +99,7 @@ function SyntheticEvent(
     }
   }
 
-  var defaultPrevented =
+  const defaultPrevented =
     nativeEvent.defaultPrevented != null
       ? nativeEvent.defaultPrevented
       : nativeEvent.returnValue === false;
@@ -115,7 +115,7 @@ function SyntheticEvent(
 Object.assign(SyntheticEvent.prototype, {
   preventDefault: function() {
     this.defaultPrevented = true;
-    var event = this.nativeEvent;
+    const event = this.nativeEvent;
     if (!event) {
       return;
     }
@@ -129,7 +129,7 @@ Object.assign(SyntheticEvent.prototype, {
   },
 
   stopPropagation: function() {
-    var event = this.nativeEvent;
+    const event = this.nativeEvent;
     if (!event) {
       return;
     }
@@ -168,8 +168,8 @@ Object.assign(SyntheticEvent.prototype, {
    * `PooledClass` looks for `destructor` on each instance it releases.
    */
   destructor: function() {
-    var Interface = this.constructor.Interface;
-    for (var propName in Interface) {
+    const Interface = this.constructor.Interface;
+    for (const propName in Interface) {
       if (__DEV__) {
         Object.defineProperty(
           this,
@@ -180,7 +180,7 @@ Object.assign(SyntheticEvent.prototype, {
         this[propName] = null;
       }
     }
-    for (var i = 0; i < shouldBeReleasedProperties.length; i++) {
+    for (let i = 0; i < shouldBeReleasedProperties.length; i++) {
       this[shouldBeReleasedProperties[i]] = null;
     }
     if (__DEV__) {
@@ -212,11 +212,11 @@ SyntheticEvent.Interface = EventInterface;
  * @param {?object} Interface
  */
 SyntheticEvent.augmentClass = function(Class, Interface) {
-  var Super = this;
+  const Super = this;
 
-  var E = function() {};
+  const E = function() {};
   E.prototype = Super.prototype;
-  var prototype = new E();
+  const prototype = new E();
 
   Object.assign(prototype, Class.prototype);
   Class.prototype = prototype;
@@ -275,7 +275,7 @@ addEventPoolingTo(SyntheticEvent);
  * @return {object} defineProperty object
  */
 function getPooledWarningPropertyDefinition(propName, getVal) {
-  var isFunction = typeof getVal === 'function';
+  const isFunction = typeof getVal === 'function';
   return {
     configurable: true,
     set: set,
@@ -283,14 +283,16 @@ function getPooledWarningPropertyDefinition(propName, getVal) {
   };
 
   function set(val) {
-    var action = isFunction ? 'setting the method' : 'setting the property';
+    const action = isFunction ? 'setting the method' : 'setting the property';
     warn(action, 'This is effectively a no-op');
     return val;
   }
 
   function get() {
-    var action = isFunction ? 'accessing the method' : 'accessing the property';
-    var result = isFunction
+    const action = isFunction
+      ? 'accessing the method'
+      : 'accessing the property';
+    const result = isFunction
       ? 'This is a no-op function'
       : 'This is set to null';
     warn(action, result);
@@ -298,7 +300,7 @@ function getPooledWarningPropertyDefinition(propName, getVal) {
   }
 
   function warn(action, result) {
-    var warningCondition = false;
+    const warningCondition = false;
     warning(
       warningCondition,
       "This synthetic event is reused for performance reasons. If you're seeing this, " +
@@ -334,7 +336,7 @@ function getPooledEvent(dispatchConfig, targetInst, nativeEvent, nativeInst) {
 }
 
 function releasePooledEvent(event) {
-  var EventConstructor = this;
+  const EventConstructor = this;
   invariant(
     event instanceof EventConstructor,
     'Trying to release an event instance  into a pool of a different type.',
diff --git a/packages/events/TouchHistoryMath.js b/packages/events/TouchHistoryMath.js
index f6d8b6fa56..87ae368ec3 100644
--- a/packages/events/TouchHistoryMath.js
+++ b/packages/events/TouchHistoryMath.js
@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-var TouchHistoryMath = {
+const TouchHistoryMath = {
   /**
    * This code is optimized and not intended to look beautiful. This allows
    * computing of touch centroids that have moved after `touchesChangedAfter`
@@ -28,11 +28,11 @@ var TouchHistoryMath = {
     isXAxis,
     ofCurrent,
   ) {
-    var touchBank = touchHistory.touchBank;
-    var total = 0;
-    var count = 0;
+    const touchBank = touchHistory.touchBank;
+    let total = 0;
+    let count = 0;
 
-    var oneTouchData =
+    const oneTouchData =
       touchHistory.numberActiveTouches === 1
         ? touchHistory.touchBank[touchHistory.indexOfSingleActiveTouch]
         : null;
@@ -53,15 +53,15 @@ var TouchHistoryMath = {
         count = 1;
       }
     } else {
-      for (var i = 0; i < touchBank.length; i++) {
-        var touchTrack = touchBank[i];
+      for (let i = 0; i < touchBank.length; i++) {
+        const touchTrack = touchBank[i];
         if (
           touchTrack !== null &&
           touchTrack !== undefined &&
           touchTrack.touchActive &&
           touchTrack.currentTimeStamp >= touchesChangedAfter
         ) {
-          var toAdd; // Yuck, program temporarily in invalid state.
+          let toAdd; // Yuck, program temporarily in invalid state.
           if (ofCurrent && isXAxis) {
             toAdd = touchTrack.currentPageX;
           } else if (ofCurrent && !isXAxis) {
diff --git a/packages/events/__tests__/EventPluginRegistry-test.internal.js b/packages/events/__tests__/EventPluginRegistry-test.internal.js
index 3af0a78237..93f21d45ab 100644
--- a/packages/events/__tests__/EventPluginRegistry-test.internal.js
+++ b/packages/events/__tests__/EventPluginRegistry-test.internal.js
@@ -10,8 +10,8 @@
 'use strict';
 
 describe('EventPluginRegistry', () => {
-  var EventPluginRegistry;
-  var createPlugin;
+  let EventPluginRegistry;
+  let createPlugin;
 
   beforeEach(() => {
     jest.resetModuleRegistry();
@@ -27,9 +27,9 @@ describe('EventPluginRegistry', () => {
   });
 
   it('should be able to inject ordering before plugins', () => {
-    var OnePlugin = createPlugin();
-    var TwoPlugin = createPlugin();
-    var ThreePlugin = createPlugin();
+    const OnePlugin = createPlugin();
+    const TwoPlugin = createPlugin();
+    const ThreePlugin = createPlugin();
 
     EventPluginRegistry.injectEventPluginOrder(['one', 'two', 'three']);
     EventPluginRegistry.injectEventPluginsByName({
@@ -47,9 +47,9 @@ describe('EventPluginRegistry', () => {
   });
 
   it('should be able to inject plugins before and after ordering', () => {
-    var OnePlugin = createPlugin();
-    var TwoPlugin = createPlugin();
-    var ThreePlugin = createPlugin();
+    const OnePlugin = createPlugin();
+    const TwoPlugin = createPlugin();
+    const ThreePlugin = createPlugin();
 
     EventPluginRegistry.injectEventPluginsByName({
       one: OnePlugin,
@@ -67,9 +67,9 @@ describe('EventPluginRegistry', () => {
   });
 
   it('should be able to inject repeated plugins and out-of-order', () => {
-    var OnePlugin = createPlugin();
-    var TwoPlugin = createPlugin();
-    var ThreePlugin = createPlugin();
+    const OnePlugin = createPlugin();
+    const TwoPlugin = createPlugin();
+    const ThreePlugin = createPlugin();
 
     EventPluginRegistry.injectEventPluginsByName({
       one: OnePlugin,
@@ -88,7 +88,7 @@ describe('EventPluginRegistry', () => {
   });
 
   it('should throw if plugin does not implement `extractEvents`', () => {
-    var BadPlugin = {};
+    const BadPlugin = {};
 
     EventPluginRegistry.injectEventPluginOrder(['bad']);
 
@@ -103,8 +103,8 @@ describe('EventPluginRegistry', () => {
   });
 
   it('should throw if plugin does not exist in ordering', () => {
-    var OnePlugin = createPlugin();
-    var RandomPlugin = createPlugin();
+    const OnePlugin = createPlugin();
+    const RandomPlugin = createPlugin();
 
     EventPluginRegistry.injectEventPluginOrder(['one']);
 
@@ -120,7 +120,7 @@ describe('EventPluginRegistry', () => {
   });
 
   it('should throw if ordering is injected more than once', () => {
-    var pluginOrdering = [];
+    const pluginOrdering = [];
 
     EventPluginRegistry.injectEventPluginOrder(pluginOrdering);
 
@@ -133,8 +133,8 @@ describe('EventPluginRegistry', () => {
   });
 
   it('should throw if different plugins injected using same name', () => {
-    var OnePlugin = createPlugin();
-    var TwoPlugin = createPlugin();
+    const OnePlugin = createPlugin();
+    const TwoPlugin = createPlugin();
 
     EventPluginRegistry.injectEventPluginsByName({same: OnePlugin});
 
@@ -147,13 +147,13 @@ describe('EventPluginRegistry', () => {
   });
 
   it('should publish registration names of injected plugins', () => {
-    var OnePlugin = createPlugin({
+    const OnePlugin = createPlugin({
       eventTypes: {
         click: {registrationName: 'onClick'},
         focus: {registrationName: 'onFocus'},
       },
     });
-    var TwoPlugin = createPlugin({
+    const TwoPlugin = createPlugin({
       eventTypes: {
         magic: {
           phasedRegistrationNames: {
@@ -187,12 +187,12 @@ describe('EventPluginRegistry', () => {
   });
 
   it('should throw if multiple registration names collide', () => {
-    var OnePlugin = createPlugin({
+    const OnePlugin = createPlugin({
       eventTypes: {
         photoCapture: {registrationName: 'onPhotoCapture'},
       },
     });
-    var TwoPlugin = createPlugin({
+    const TwoPlugin = createPlugin({
       eventTypes: {
         photo: {
           phasedRegistrationNames: {
@@ -217,7 +217,7 @@ describe('EventPluginRegistry', () => {
   });
 
   it('should throw if an invalid event is published', () => {
-    var OnePlugin = createPlugin({
+    const OnePlugin = createPlugin({
       eventTypes: {
         badEvent: {
           /* missing configuration */
diff --git a/packages/events/__tests__/ResponderEventPlugin-test.internal.js b/packages/events/__tests__/ResponderEventPlugin-test.internal.js
index 15cdd32617..e9283628e1 100644
--- a/packages/events/__tests__/ResponderEventPlugin-test.internal.js
+++ b/packages/events/__tests__/ResponderEventPlugin-test.internal.js
@@ -9,12 +9,12 @@
 
 'use strict';
 
-var {HostComponent} = require('shared/ReactTypeOfWork');
+const {HostComponent} = require('shared/ReactTypeOfWork');
 
-var EventPluginHub;
-var ResponderEventPlugin;
+let EventPluginHub;
+let ResponderEventPlugin;
 
-var touch = function(nodeHandle, i) {
+const touch = function(nodeHandle, i) {
   return {target: nodeHandle, identifier: i};
 };
 
@@ -25,7 +25,7 @@ var touch = function(nodeHandle, i) {
  * @return {TouchEvent} Model of a touch event that is compliant with responder
  * system plugin.
  */
-var touchEvent = function(nodeHandle, touches, changedTouches) {
+const touchEvent = function(nodeHandle, touches, changedTouches) {
   return {
     target: nodeHandle,
     changedTouches: changedTouches,
@@ -33,18 +33,18 @@ var touchEvent = function(nodeHandle, touches, changedTouches) {
   };
 };
 
-var subsequence = function(arr, indices) {
-  var ret = [];
-  for (var i = 0; i < indices.length; i++) {
-    var index = indices[i];
+const subsequence = function(arr, indices) {
+  const ret = [];
+  for (let i = 0; i < indices.length; i++) {
+    const index = indices[i];
     ret.push(arr[index]);
   }
   return ret;
 };
 
-var antiSubsequence = function(arr, indices) {
-  var ret = [];
-  for (var i = 0; i < arr.length; i++) {
+const antiSubsequence = function(arr, indices) {
+  const ret = [];
+  for (let i = 0; i < arr.length; i++) {
     if (indices.indexOf(i) === -1) {
       ret.push(arr[i]);
     }
@@ -56,16 +56,16 @@ var antiSubsequence = function(arr, indices) {
  * Helper for creating touch test config data.
  * @param allTouchHandles
  */
-var _touchConfig = function(
+const _touchConfig = function(
   topType,
   targetNodeHandle,
   allTouchHandles,
   changedIndices,
   eventTarget,
 ) {
-  var allTouchObjects = allTouchHandles.map(touch);
-  var changedTouchObjects = subsequence(allTouchObjects, changedIndices);
-  var activeTouchObjects = topType === 'topTouchStart'
+  const allTouchObjects = allTouchHandles.map(touch);
+  const changedTouchObjects = subsequence(allTouchObjects, changedIndices);
+  const activeTouchObjects = topType === 'topTouchStart'
     ? allTouchObjects
     : topType === 'topTouchMove'
         ? allTouchObjects
@@ -104,7 +104,7 @@ var _touchConfig = function(
  * @return {object} Config data used by test cases for extracting responder
  * events.
  */
-var startConfig = function(nodeHandle, allTouchHandles, changedIndices) {
+const startConfig = function(nodeHandle, allTouchHandles, changedIndices) {
   return _touchConfig(
     'topTouchStart',
     nodeHandle,
@@ -117,7 +117,7 @@ var startConfig = function(nodeHandle, allTouchHandles, changedIndices) {
 /**
  * @see `startConfig`
  */
-var moveConfig = function(nodeHandle, allTouchHandles, changedIndices) {
+const moveConfig = function(nodeHandle, allTouchHandles, changedIndices) {
   return _touchConfig(
     'topTouchMove',
     nodeHandle,
@@ -130,7 +130,7 @@ var moveConfig = function(nodeHandle, allTouchHandles, changedIndices) {
 /**
  * @see `startConfig`
  */
-var endConfig = function(nodeHandle, allTouchHandles, changedIndices) {
+const endConfig = function(nodeHandle, allTouchHandles, changedIndices) {
   return _touchConfig(
     'topTouchEnd',
     nodeHandle,
@@ -167,9 +167,9 @@ var endConfig = function(nodeHandle, allTouchHandles, changedIndices) {
  * ever invoked).
  *
  */
-var NA = -1;
-var oneEventLoopTestConfig = function(readableIDToID) {
-  var ret = {
+const NA = -1;
+const oneEventLoopTestConfig = function(readableIDToID) {
+  const ret = {
     // Negotiation
     scrollShouldSetResponder: {bubbled: {}, captured: {}},
     startShouldSetResponder: {bubbled: {}, captured: {}},
@@ -185,8 +185,8 @@ var oneEventLoopTestConfig = function(readableIDToID) {
     responderEnd: {},
     responderRelease: {},
   };
-  for (var eventName in ret) {
-    for (var readableNodeName in readableIDToID) {
+  for (const eventName in ret) {
+    for (const readableNodeName in readableIDToID) {
       if (ret[eventName].bubbled) {
         // Two phase
         ret[eventName].bubbled[readableNodeName] = {
@@ -215,9 +215,9 @@ var oneEventLoopTestConfig = function(readableIDToID) {
  * @param {object} eventTestConfig
  * @param {object} readableIDToID
  */
-var registerTestHandlers = function(eventTestConfig, readableIDToID) {
-  var runs = {dispatchCount: 0};
-  var neverFire = function(readableID, registrationName) {
+const registerTestHandlers = function(eventTestConfig, readableIDToID) {
+  const runs = {dispatchCount: 0};
+  const neverFire = function(readableID, registrationName) {
     runs.dispatchCount++;
     expect('').toBe(
       'Event type: ' +
@@ -230,11 +230,11 @@ var registerTestHandlers = function(eventTestConfig, readableIDToID) {
     );
   };
 
-  var registerOneEventType = function(registrationName, eventTypeTestConfig) {
-    for (var readableID in eventTypeTestConfig) {
-      var nodeConfig = eventTypeTestConfig[readableID];
-      var id = readableIDToID[readableID];
-      var handler = nodeConfig.order === NA
+  const registerOneEventType = function(registrationName, eventTypeTestConfig) {
+    for (const readableID in eventTypeTestConfig) {
+      const nodeConfig = eventTypeTestConfig[readableID];
+      const id = readableIDToID[readableID];
+      const handler = nodeConfig.order === NA
         ? neverFire.bind(null, readableID, registrationName)
         : // We partially apply readableID and nodeConfig, as they change in the
           // parent closure across iterations.
@@ -250,9 +250,9 @@ var registerTestHandlers = function(eventTestConfig, readableIDToID) {
       putListener(getInstanceFromNode(id), registrationName, handler);
     }
   };
-  for (var eventName in eventTestConfig) {
-    var oneEventTypeTestConfig = eventTestConfig[eventName];
-    var hasTwoPhase = !!oneEventTypeTestConfig.bubbled;
+  for (const eventName in eventTestConfig) {
+    const oneEventTypeTestConfig = eventTestConfig[eventName];
+    const hasTwoPhase = !!oneEventTypeTestConfig.bubbled;
     if (hasTwoPhase) {
       registerOneEventType(
         ResponderEventPlugin.eventTypes[eventName].phasedRegistrationNames
@@ -274,16 +274,16 @@ var registerTestHandlers = function(eventTestConfig, readableIDToID) {
   return runs;
 };
 
-var run = function(config, hierarchyConfig, nativeEventConfig) {
-  var max = NA;
-  var searchForMax = function(nodeConfig) {
-    for (var readableID in nodeConfig) {
-      var order = nodeConfig[readableID].order;
+const run = function(config, hierarchyConfig, nativeEventConfig) {
+  let max = NA;
+  const searchForMax = function(nodeConfig) {
+    for (const readableID in nodeConfig) {
+      const order = nodeConfig[readableID].order;
       max = order > max ? order : max;
     }
   };
-  for (var eventName in config) {
-    var eventConfig = config[eventName];
+  for (const eventName in config) {
+    const eventConfig = config[eventName];
     if (eventConfig.bubbled) {
       searchForMax(eventConfig.bubbled);
       searchForMax(eventConfig.captured);
@@ -293,10 +293,10 @@ var run = function(config, hierarchyConfig, nativeEventConfig) {
   }
 
   // Register the handlers
-  var runData = registerTestHandlers(config, hierarchyConfig);
+  const runData = registerTestHandlers(config, hierarchyConfig);
 
   // Trigger the event
-  var extractedEvents = ResponderEventPlugin.extractEvents(
+  const extractedEvents = ResponderEventPlugin.extractEvents(
     nativeEventConfig.topLevelType,
     nativeEventConfig.targetInst,
     nativeEventConfig.nativeEvent,
@@ -315,32 +315,32 @@ var run = function(config, hierarchyConfig, nativeEventConfig) {
   ); // +1 for extra ++
 };
 
-var GRANDPARENT_HOST_NODE = {};
-var PARENT_HOST_NODE = {};
-var CHILD_HOST_NODE = {};
-var CHILD_HOST_NODE2 = {};
+const GRANDPARENT_HOST_NODE = {};
+const PARENT_HOST_NODE = {};
+const CHILD_HOST_NODE = {};
+const CHILD_HOST_NODE2 = {};
 
 // These intentionally look like Fibers. ReactTreeTraversal depends on their field names.
 // TODO: we could test this with regular DOM nodes (and real fibers) instead.
-var GRANDPARENT_INST = {
+const GRANDPARENT_INST = {
   return: null,
   tag: HostComponent,
   stateNode: GRANDPARENT_HOST_NODE,
   memoizedProps: {},
 };
-var PARENT_INST = {
+const PARENT_INST = {
   return: GRANDPARENT_INST,
   tag: HostComponent,
   stateNode: PARENT_HOST_NODE,
   memoizedProps: {},
 };
-var CHILD_INST = {
+const CHILD_INST = {
   return: PARENT_INST,
   tag: HostComponent,
   stateNode: CHILD_HOST_NODE,
   memoizedProps: {},
 };
-var CHILD_INST2 = {
+const CHILD_INST2 = {
   return: PARENT_INST,
   tag: HostComponent,
   stateNode: CHILD_HOST_NODE2,
@@ -352,13 +352,13 @@ PARENT_HOST_NODE.testInstance = PARENT_INST;
 CHILD_HOST_NODE.testInstance = CHILD_INST;
 CHILD_HOST_NODE2.testInstance = CHILD_INST2;
 
-var three = {
+const three = {
   grandParent: GRANDPARENT_HOST_NODE,
   parent: PARENT_HOST_NODE,
   child: CHILD_HOST_NODE,
 };
 
-var siblings = {
+const siblings = {
   parent: PARENT_HOST_NODE,
   childOne: CHILD_HOST_NODE,
   childTwo: CHILD_HOST_NODE2,
@@ -411,7 +411,7 @@ describe('ResponderEventPlugin', () => {
   });
 
   it('should do nothing when no one wants to respond', () => {
-    var config = oneEventLoopTestConfig(three);
+    let config = oneEventLoopTestConfig(three);
     config.startShouldSetResponder.captured.grandParent = {
       order: 0,
       returnVal: false,
@@ -448,7 +448,7 @@ describe('ResponderEventPlugin', () => {
    */
 
   it('should grant responder grandParent while capturing', () => {
-    var config = oneEventLoopTestConfig(three);
+    let config = oneEventLoopTestConfig(three);
     config.startShouldSetResponder.captured.grandParent = {
       order: 0,
       returnVal: true,
@@ -468,7 +468,7 @@ describe('ResponderEventPlugin', () => {
   });
 
   it('should grant responder parent while capturing', () => {
-    var config = oneEventLoopTestConfig(three);
+    let config = oneEventLoopTestConfig(three);
     config.startShouldSetResponder.captured.grandParent = {
       order: 0,
       returnVal: false,
@@ -492,7 +492,7 @@ describe('ResponderEventPlugin', () => {
   });
 
   it('should grant responder child while capturing', () => {
-    var config = oneEventLoopTestConfig(three);
+    let config = oneEventLoopTestConfig(three);
     config.startShouldSetResponder.captured.grandParent = {
       order: 0,
       returnVal: false,
@@ -517,7 +517,7 @@ describe('ResponderEventPlugin', () => {
   });
 
   it('should grant responder child while bubbling', () => {
-    var config = oneEventLoopTestConfig(three);
+    let config = oneEventLoopTestConfig(three);
     config.startShouldSetResponder.captured.grandParent = {
       order: 0,
       returnVal: false,
@@ -546,7 +546,7 @@ describe('ResponderEventPlugin', () => {
   });
 
   it('should grant responder parent while bubbling', () => {
-    var config = oneEventLoopTestConfig(three);
+    let config = oneEventLoopTestConfig(three);
     config.startShouldSetResponder.captured.grandParent = {
       order: 0,
       returnVal: false,
@@ -576,7 +576,7 @@ describe('ResponderEventPlugin', () => {
   });
 
   it('should grant responder grandParent while bubbling', () => {
-    var config = oneEventLoopTestConfig(three);
+    let config = oneEventLoopTestConfig(three);
     config.startShouldSetResponder.captured.grandParent = {
       order: 0,
       returnVal: false,
@@ -618,7 +618,7 @@ describe('ResponderEventPlugin', () => {
    */
 
   it('should grant responder grandParent while capturing move', () => {
-    var config = oneEventLoopTestConfig(three);
+    let config = oneEventLoopTestConfig(three);
 
     config.startShouldSetResponder.captured.grandParent = {order: 0};
     config.startShouldSetResponder.captured.parent = {order: 1};
@@ -648,7 +648,7 @@ describe('ResponderEventPlugin', () => {
   });
 
   it('should grant responder parent while capturing move', () => {
-    var config = oneEventLoopTestConfig(three);
+    let config = oneEventLoopTestConfig(three);
 
     config.startShouldSetResponder.captured.grandParent = {order: 0};
     config.startShouldSetResponder.captured.parent = {order: 1};
@@ -679,7 +679,7 @@ describe('ResponderEventPlugin', () => {
   });
 
   it('should grant responder child while capturing move', () => {
-    var config = oneEventLoopTestConfig(three);
+    let config = oneEventLoopTestConfig(three);
 
     config.startShouldSetResponder.captured.grandParent = {order: 0};
     config.startShouldSetResponder.captured.parent = {order: 1};
@@ -714,7 +714,7 @@ describe('ResponderEventPlugin', () => {
   });
 
   it('should grant responder child while bubbling move', () => {
-    var config = oneEventLoopTestConfig(three);
+    let config = oneEventLoopTestConfig(three);
 
     config.startShouldSetResponder.captured.grandParent = {order: 0};
     config.startShouldSetResponder.captured.parent = {order: 1};
@@ -750,7 +750,7 @@ describe('ResponderEventPlugin', () => {
   });
 
   it('should grant responder parent while bubbling move', () => {
-    var config = oneEventLoopTestConfig(three);
+    let config = oneEventLoopTestConfig(three);
 
     config.startShouldSetResponder.captured.grandParent = {order: 0};
     config.startShouldSetResponder.captured.parent = {order: 1};
@@ -787,7 +787,7 @@ describe('ResponderEventPlugin', () => {
   });
 
   it('should grant responder grandParent while bubbling move', () => {
-    var config = oneEventLoopTestConfig(three);
+    let config = oneEventLoopTestConfig(three);
 
     config.startShouldSetResponder.captured.grandParent = {order: 0};
     config.startShouldSetResponder.captured.parent = {order: 1};
@@ -833,7 +833,7 @@ describe('ResponderEventPlugin', () => {
    */
 
   it('should bubble negotiation to first common ancestor of responder', () => {
-    var config = oneEventLoopTestConfig(three);
+    let config = oneEventLoopTestConfig(three);
     config.startShouldSetResponder.captured.grandParent = {
       order: 0,
       returnVal: false,
@@ -875,7 +875,7 @@ describe('ResponderEventPlugin', () => {
   });
 
   it('should bubble negotiation to first common ancestor of responder then transfer', () => {
-    var config = oneEventLoopTestConfig(three);
+    let config = oneEventLoopTestConfig(three);
     config.startShouldSetResponder.captured.grandParent = {
       order: 0,
       returnVal: false,
@@ -932,7 +932,7 @@ describe('ResponderEventPlugin', () => {
    */
   it('should negotiate with deepest target on second touch if nothing is responder', () => {
     // Initially nothing wants to become the responder
-    var config = oneEventLoopTestConfig(three);
+    let config = oneEventLoopTestConfig(three);
     config.startShouldSetResponder.captured.grandParent = {
       order: 0,
       returnVal: false,
@@ -1080,7 +1080,7 @@ describe('ResponderEventPlugin', () => {
    */
   it('should negotiate until first common ancestor when there are siblings', () => {
     // Initially nothing wants to become the responder
-    var config = oneEventLoopTestConfig(siblings);
+    let config = oneEventLoopTestConfig(siblings);
     config.startShouldSetResponder.captured.parent = {
       order: 0,
       returnVal: false,
@@ -1119,7 +1119,7 @@ describe('ResponderEventPlugin', () => {
     };
     config.responderStart.childOne = {order: 2};
 
-    var touchConfig = startConfig(
+    const touchConfig = startConfig(
       siblings.childTwo,
       [siblings.childOne, siblings.childTwo],
       [1],
@@ -1174,7 +1174,7 @@ describe('ResponderEventPlugin', () => {
 
   it('should notify of being rejected. responderStart/Move happens on current responder', () => {
     // Initially nothing wants to become the responder
-    var config = oneEventLoopTestConfig(three);
+    let config = oneEventLoopTestConfig(three);
     config.startShouldSetResponder.captured.grandParent = {
       order: 0,
       returnVal: false,
@@ -1213,7 +1213,7 @@ describe('ResponderEventPlugin', () => {
     // The start/move should occur on the original responder if new one is rejected
     config.responderMove.child = {order: 6};
 
-    var touchConfig = moveConfig(three.child, [three.child], [0]);
+    let touchConfig = moveConfig(three.child, [three.child], [0]);
     run(config, three, touchConfig);
     expect(ResponderEventPlugin._getResponder()).toBe(
       getInstanceFromNode(three.child),
@@ -1244,7 +1244,7 @@ describe('ResponderEventPlugin', () => {
 
   it('should negotiate scroll', () => {
     // Initially nothing wants to become the responder
-    var config = oneEventLoopTestConfig(three);
+    let config = oneEventLoopTestConfig(three);
     config.startShouldSetResponder.captured.grandParent = {
       order: 0,
       returnVal: false,
@@ -1325,7 +1325,7 @@ describe('ResponderEventPlugin', () => {
 
   it('should cancel correctly', () => {
     // Initially our child becomes responder
-    var config = oneEventLoopTestConfig(three);
+    let config = oneEventLoopTestConfig(three);
     config.startShouldSetResponder.captured.grandParent = {
       order: 0,
       returnVal: false,
@@ -1351,7 +1351,7 @@ describe('ResponderEventPlugin', () => {
     config.responderEnd.child = {order: 0};
     config.responderTerminate.child = {order: 1};
 
-    var nativeEvent = _touchConfig(
+    const nativeEvent = _touchConfig(
       'topTouchCancel',
       three.child,
       [three.child],
@@ -1364,10 +1364,10 @@ describe('ResponderEventPlugin', () => {
   it('should determine the first common ancestor correctly', () => {
     // This test was moved here from the ReactTreeTraversal test since only the 
     // ResponderEventPlugin uses `getLowestCommonAncestor`
-    var React = require('react');
-    var ReactTestUtils = require('react-dom/test-utils');
-    var ReactTreeTraversal = require('shared/ReactTreeTraversal');
-    var ReactDOMComponentTree = require('../../react-dom/src/client/ReactDOMComponentTree');
+    const React = require('react');
+    const ReactTestUtils = require('react-dom/test-utils');
+    const ReactTreeTraversal = require('shared/ReactTreeTraversal');
+    const ReactDOMComponentTree = require('../../react-dom/src/client/ReactDOMComponentTree');
 
     class ChildComponent extends React.Component {
       render() {
@@ -1394,9 +1394,9 @@ describe('ResponderEventPlugin', () => {
       }
     }
 
-    var parent = ReactTestUtils.renderIntoDocument(<ParentComponent />);
+    const parent = ReactTestUtils.renderIntoDocument(<ParentComponent />);
 
-    var ancestors = [
+    const ancestors = [
       // Common ancestor with self is self.
       {
         one: parent.refs.P_P1_C1.refs.DIV_1,
@@ -1436,10 +1436,10 @@ describe('ResponderEventPlugin', () => {
         com: parent.refs.P,
       },
     ];
-    var i;
+    let i;
     for (i = 0; i < ancestors.length; i++) {
-      var plan = ancestors[i];
-      var firstCommon = ReactTreeTraversal.getLowestCommonAncestor(
+      const plan = ancestors[i];
+      const firstCommon = ReactTreeTraversal.getLowestCommonAncestor(
         ReactDOMComponentTree.getInstanceFromNode(plan.one),
         ReactDOMComponentTree.getInstanceFromNode(plan.two),
       );
diff --git a/packages/events/__tests__/accumulateInto-test.internal.js b/packages/events/__tests__/accumulateInto-test.internal.js
index e04bba5d36..2ee9d547c6 100644
--- a/packages/events/__tests__/accumulateInto-test.internal.js
+++ b/packages/events/__tests__/accumulateInto-test.internal.js
@@ -9,7 +9,7 @@
 
 'use strict';
 
-var accumulateInto;
+let accumulateInto;
 
 describe('accumulateInto', () => {
   beforeEach(() => {
@@ -25,23 +25,23 @@ describe('accumulateInto', () => {
   });
 
   it('returns the second item if first is null', () => {
-    var a = [];
+    const a = [];
     expect(accumulateInto(null, a)).toBe(a);
   });
 
   it('merges the second into the first if first item is an array', () => {
-    var a = [1, 2];
-    var b = [3, 4];
+    const a = [1, 2];
+    const b = [3, 4];
     accumulateInto(a, b);
     expect(a).toEqual([1, 2, 3, 4]);
     expect(b).toEqual([3, 4]);
-    var c = [1];
+    const c = [1];
     accumulateInto(c, 2);
     expect(c).toEqual([1, 2]);
   });
 
   it('returns a new array if first or both items are scalar', () => {
-    var a = [2];
+    const a = [2];
     expect(accumulateInto(1, a)).toEqual([1, 2]);
     expect(a).toEqual([2]);
     expect(accumulateInto(1, 2)).toEqual([1, 2]);