Add ability to supply custom cloing logic

Author: watson

README.md

@@ -14,7 +14,7 @@ Install
 Usage
 -----
 
-	var deepExtend = require('deep-extend');
+	var deepExtend = require('deep-extend')();
 	var obj1 = {
 		a: 1,
 		b: 2,
@@ -56,3 +56,44 @@ Usage
 	  e: { one: 1, two: 2 },
 	  h: /abc/g }
 	*/
+
+Custom Clone Logic
+------------------
+
+The deep-extend module will by default extend all types of objects. But
+if you clone a custom object it will no longer be an instance of its
+original class. If this is important to you, you can supply a custom cloning
+function which you can use to implement your own cloning logic.
+
+It will be called for every value in the object. If you return a falsy
+value the default behavior of deep-extend will be used. If you return a
+truthy value that value will be used as a replacement for the original
+value.
+
+	var Foo = function(val) {
+		this.foo = val;
+	};
+	var Bar = function(val) {
+		this.bar = val;
+	};
+
+	var cloner = function (obj) {
+		// if given an instance of Foo, return a clone of it
+		if (obj instanceof Foo) return new Foo(obj.foo);
+	};
+
+	var deepExtend = require('deep-extend')(cloner);
+	var obj = {
+		a: new Foo(1),
+		b: new Bar(2)
+	};
+
+	var clone = deepExtend({}, obj);
+
+	console.log(clone);
+	/*
+	{ a: { foo: 1 },
+	  b: { bar: 2 } }
+	*/
+	console.log(clone.a instanceof Foo); // true
+	console.log(clone.b instanceof Bar); // false

index.js

@@ -32,62 +32,73 @@
  * If you wish to clone object, simply use that:
  *  deepExtend({}, yourObj_1, [yourObj_N]) - first arg is new empty object
  */
-var deepExtend = module.exports = function (/*obj_1, [obj_2], [obj_N]*/) {
-	if (arguments.length < 1 || typeof arguments[0] !== 'object') {
-		return false;
-	}
 
-	if (arguments.length < 2) return arguments[0];
+var noop = function () {};
 
-	var target = arguments[0];
+module.exports = function (cloner) {
+	if (!cloner) cloner = noop;
 
-	// convert arguments to array and cut off target object
-	var args = Array.prototype.slice.call(arguments, 1);
+	return function deepExtend(/*obj_1, [obj_2], [obj_N]*/) {
+		if (arguments.length < 1 || typeof arguments[0] !== 'object') {
+			return false;
+		}
 
-	var key, val, src, clone, tmpBuf;
+		if (arguments.length < 2) return arguments[0];
 
-	args.forEach(function (obj) {
-		if (typeof obj !== 'object') return;
+		var target = arguments[0];
 
-		for (key in obj) {
-			if ( ! (key in obj)) continue;
+		// convert arguments to array and cut off target object
+		var args = Array.prototype.slice.call(arguments, 1);
 
-			src = target[key];
-			val = obj[key];
+		var key, val, src, clone, tmpBuf, custom;
 
-			if (val === target) continue;
+		args.forEach(function (obj) {
+			if (typeof obj !== 'object') return;
 
-			if (typeof val !== 'object' || val === null) {
-				target[key] = val;
-				continue;
-			} else if (val instanceof Buffer) {
-				tmpBuf = new Buffer(val.length);
-				val.copy(tmpBuf);
-				target[key] = tmpBuf;
-				continue;
-			} else if (val instanceof Date) {
-				target[key] = new Date(val.getTime());
-				continue;
-			} else if (val instanceof RegExp) {
-				target[key] = new RegExp(val);
-				continue;
-			}
+			for (key in obj) {
+				if ( ! (key in obj)) continue;
 
-			if (typeof src !== 'object' || src === null) {
-				clone = (Array.isArray(val)) ? [] : {};
-				target[key] = deepExtend(clone, val);
-				continue;
-			}
+				src = target[key];
+				val = obj[key];
+
+				if (val === target) continue;
 
-			if (Array.isArray(val)) {
-				clone = (Array.isArray(src)) ? src : [];
-			} else {
-				clone = (!Array.isArray(src)) ? src : {};
+				if (custom = cloner(val)) {
+					target[key] = custom;
+					continue;
+				} else if (typeof val !== 'object' || val === null) {
+					target[key] = val;
+					continue;
+				} else if (val instanceof Buffer) {
+					tmpBuf = new Buffer(val.length);
+					val.copy(tmpBuf);
+					target[key] = tmpBuf;
+					continue;
+				} else if (val instanceof Date) {
+					target[key] = new Date(val.getTime());
+					continue;
+				} else if (val instanceof RegExp) {
+					target[key] = new RegExp(val);
+					continue;
+				}
+
+				if (typeof src !== 'object' || src === null) {
+					clone = (Array.isArray(val)) ? [] : {};
+					target[key] = deepExtend(clone, val);
+					continue;
+				}
+
+				if (Array.isArray(val)) {
+					clone = (Array.isArray(src)) ? src : [];
+				} else {
+					clone = (!Array.isArray(src)) ? src : {};
+				}
+
+				target[key] = deepExtend(clone, val);
 			}
+		});
 
-			target[key] = deepExtend(clone, val);
-		}
-	});
+		return target;
+	}
+};
 
-	return target;
-}