add _.cloneDeep

test/objects.js

@@ -286,6 +286,41 @@
     assert.strictEqual(_.clone(null), null, 'non objects should not be changed by clone');
   });
 
+  QUnit.test('cloneDeep', function(assert) {
+    var source = {
+      str: 'str',
+      num: 1,
+      bool: false,
+      list: [1, 2, 3],
+      obj: {a: 'a', b: 'b'},
+      nu: null,
+      und: void 0
+    };
+    var clone = _.cloneDeep(source);
+    assert.strictEqual(clone.str, 'str', 'can clone string value from source');
+    assert.strictEqual(clone.num, 1, 'can clone number value from source');
+    assert.strictEqual(clone.bool, false, 'can clone boolean value from source');
+    assert.deepEqual(clone.list, [1, 2, 3], 'can clone array from source');
+    assert.deepEqual(clone.obj, {a: 'a', b: 'b'}, 'can clone object from source');
+    assert.deepEqual(clone.nu, null, 'can clone null value from source');
+    assert.deepEqual(clone.und, void 0, 'can clone undefined value from source');
+
+    assert.notStrictEqual(clone.list, source.list, 'refers to a copy of the original array');
+    assert.notStrictEqual(clone.obj, source.obj, 'refers to a copy of the original object');
+
+    function F() {}
+    F.prototype = {a: 'a'};
+    var subObj = new F();
+    subObj.b = 'b';
+    clone = _.cloneDeep(subObj);
+    assert.deepEqual(clone, {a: 'a', b: 'b'}, 'copies all properties from source');
+
+    source = {a: 'a'};
+    source.obj = source;
+    clone = _.cloneDeep(source);
+    assert.deepEqual(clone.obj.a, 'a', 'can deal with circular references cases');
+  });
+
   QUnit.test('create', function(assert) {
     var Parent = function() {};
     Parent.prototype = {foo: function() {}, bar: 2};

underscore.js

@@ -1158,6 +1158,37 @@
     return _.isArray(obj) ? obj.slice() : _.extend({}, obj);
   };
 
+  // Create a (deep-cloned) duplicate of an object.
+  var cloneDeep = function(obj, stack) {
+    if (!_.isObject(obj)) {
+      return obj;
+    }
+    var keys = !isArrayLike(obj) && _.allKeys(obj),
+        length = (keys || obj).length,
+        result = keys ? {} : [];
+
+    if (!stack) {
+      stack = [[], []];
+    }
+    var stacked = _.indexOf(stack[0], obj);
+    if (stacked > -1) {
+      return stack[1][stacked];
+    }
+    stack[0].push(obj);
+    stack[1].push(result);
+
+    for (var i = 0; i < length; i++) {
+      var key = keys ? keys[i] : i;
+      result[key] = cloneDeep(obj[key], stack);
+    }
+
+    return result;
+  };
+
+  _.cloneDeep = function(obj) {
+    return cloneDeep(obj);
+  };
+
   // Invokes interceptor with the obj, and then returns obj.
   // The primary purpose of this method is to "tap into" a method chain, in
   // order to perform operations on intermediate results within the chain.