sjfloat
diff --git a/‎__tests__/merge.ts
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+9Lines changed: 9 additions & 0 deletions b/‎__tests__/merge.ts
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+9Lines changed: 9 additions & 0 deletions
diff --git a/‎dist/immutable.d.ts
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+8-8Lines changed: 8 additions & 8 deletions b/‎dist/immutable.d.ts
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+8-8Lines changed: 8 additions & 8 deletions
diff --git a/‎dist/immutable.js
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+3-3Lines changed: 3 additions & 3 deletions b/‎dist/immutable.js
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+3-3Lines changed: 3 additions & 3 deletions
@@ -40,6 +40,15 @@ describe('merge', () => {
     expect(m1.mergeWith((a, b) => a + b, m2)).is(I.Map({a:1,b:22,c:3,d:10,e:30}));
   })
 
+  it('provides key as the third argument of merge function', () => {
+    var m1 = I.Map({id:'temp',  b:2,  c:3});
+    var m2 = I.Map({id:10,  b:20, e:30});
+    var add = (a, b) => a + b
+    expect(
+      m1.mergeWith((a, b, key) => key !== 'id' ? add(a, b) : b, m2)
+    ).is(I.Map({id:10,b:22,c:3,e:30}));
+  })
+
   it('deep merges two maps', () => {
     var m1 = I.fromJS({a:{b:{c:1,d:2}}});
     var m2 = I.fromJS({a:{b:{c:10,e:20},f:30},g:40});
 
@@ -224,11 +224,11 @@ declare module 'immutable' {
      * @see `Map#mergeWith`
      */
     mergeWith(
-      merger: (previous?: T, next?: T) => T,
+      merger: (previous?: T, next?: T, key?: number) => T,
       ...iterables: IndexedIterable<T>[]
     ): List<T>;
     mergeWith(
-      merger: (previous?: T, next?: T) => T,
+      merger: (previous?: T, next?: T, key?: number) => T,
       ...iterables: Array<T>[]
     ): List<T>;
 
@@ -242,11 +242,11 @@ declare module 'immutable' {
      * @see `Map#mergeDeepWith`
      */
     mergeDeepWith(
-      merger: (previous?: T, next?: T) => T,
+      merger: (previous?: T, next?: T, key?: number) => T,
       ...iterables: IndexedIterable<T>[]
     ): List<T>;
     mergeDeepWith(
-      merger: (previous?: T, next?: T) => T,
+      merger: (previous?: T, next?: T, key?: number) => T,
       ...iterables: Array<T>[]
     ): List<T>;
 
@@ -478,11 +478,11 @@ declare module 'immutable' {
      *
      */
     mergeWith(
-      merger: (previous?: V, next?: V) => V,
+      merger: (previous?: V, next?: V, key?: K) => V,
       ...iterables: Iterable<K, V>[]
     ): Map<K, V>;
     mergeWith(
-      merger: (previous?: V, next?: V) => V,
+      merger: (previous?: V, next?: V, key?: K) => V,
       ...iterables: {[key: string]: V}[]
     ): Map<string, V>;
 
@@ -509,11 +509,11 @@ declare module 'immutable' {
      *
      */
     mergeDeepWith(
-      merger: (previous?: V, next?: V) => V,
+      merger: (previous?: V, next?: V, key?: K) => V,
       ...iterables: Iterable<K, V>[]
     ): Map<K, V>;
     mergeDeepWith(
-      merger: (previous?: V, next?: V) => V,
+      merger: (previous?: V, next?: V, key?: K) => V,
       ...iterables: {[key: string]: V}[]
     ): Map<string, V>;
 
 
@@ -2411,10 +2411,10 @@
   }
 
   function deepMerger(merger) {
-    return function(existing, value) 
+    return function(existing, value, key) 
       {return existing && existing.mergeDeepWith && isIterable(value) ?
         existing.mergeDeepWith(merger, value) :
-        merger ? merger(existing, value) : value};
+        merger ? merger(existing, value, key) : value};
   }
 
   function mergeIntoCollectionWith(collection, merger, iters) {
@@ -2429,7 +2429,7 @@
       var mergeIntoMap = merger ?
         function(value, key)  {
           collection.update(key, NOT_SET, function(existing )
-            {return existing === NOT_SET ? value : merger(existing, value)}
+            {return existing === NOT_SET ? value : merger(existing, value, key)}
           );
         } :
         function(value, key)  {