githubsheng
diff --git a/‎__tests__/Record.ts
Lines changed: 20 additions & 0 deletions b/‎__tests__/Record.ts
Lines changed: 20 additions & 0 deletions
diff --git a/‎dist/immutable.js
Lines changed: 6 additions & 0 deletions b/‎dist/immutable.js
Lines changed: 6 additions & 0 deletions
@@ -94,4 +94,24 @@ describe('Record', () => {
     expect(t.get('c')).toBeUndefined();
   })
 
+  it('returns itself when setting identical values', () => {
+    var MyType = Record({a:1, b:2});
+    var t1 = new MyType;
+    var t2 = new MyType({a: 1});
+    var t3 = t1.set('a', 1);
+    var t4 = t2.set('a', 1);
+    expect(t3).toBe(t1);
+    expect(t4).toBe(t2);
+  })
+
+  it('returns new record when setting new values', () => {
+    var MyType = Record({a:1, b:2});
+    var t1 = new MyType;
+    var t2 = new MyType({a: 1});
+    var t3 = t1.set('a', 3);
+    var t4 = t2.set('a', 3);
+    expect(t3).not.toBe(t1);
+    expect(t4).not.toBe(t2);
+  })
+
 });
@@ -3682,6 +3682,12 @@
       if (!this.has(k)) {
         throw new Error('Cannot set unknown key "' + k + '" on ' + recordName(this));
       }
+      if (this._map && !this._map.has(k)) {
+        var defaultVal = this._defaultValues[k];
+        if (v === defaultVal) {
+          return this;
+        }
+      }
       var newMap = this._map && this._map.set(k, v);
       if (this.__ownerID || newMap === this._map) {
         return this;