diff --git a/js/js.libraries/src/core/collections/AbstractSet.kt b/js/js.libraries/src/core/collections/AbstractSet.kt
new file mode 100644
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+++ b/js/js.libraries/src/core/collections/AbstractSet.kt
@@ -0,0 +1,35 @@
+/*
+ * Copyright 2010-2016 JetBrains s.r.o.
+ *
+ * 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.
+ */
+package kotlin.collections
+
+abstract class AbstractSet<E> protected constructor() : AbstractCollection<E>(), MutableSet<E> {
+
+    override fun equals(other: Any?): Boolean {
+        if (other === this) return true
+        if (other !is Set<*>) return false
+        if (other.size != size) return false
+        return containsAll(other)
+    }
+
+    override fun hashCode(): Int {
+        var hashCode = 0
+        for (element in this) {
+            hashCode = (hashCode + (element?.hashCode() ?: 0)) or 0
+        }
+        return hashCode
+    }
+
+}
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