Improve clone() performance. Closes #344

Author: hueniverse

lib/clone.js

@@ -36,48 +36,26 @@ module.exports = internals.clone = function (obj, options = {}, _seen = null) {
         }
     }
 
+    // Built-in object types
+
     const baseProto = Types.getInternalProto(obj);
-    let newObj;
-
-    switch (baseProto) {
-        case Types.buffer:
-            return Buffer && Buffer.from(obj);              // $lab:coverage:ignore$
-
-        case Types.date:
-            return new Date(obj.getTime());
-
-        case Types.regex:
-            return new RegExp(obj);
-
-        case Types.array:
-            newObj = [];
-            break;
-
-        default:
-            if (options.prototype !== false) {              // Defaults to true
-                const proto = Object.getPrototypeOf(obj);
-                if (proto &&
-                    proto.isImmutable) {
-
-                    return obj;
-                }
-
-                if (internals.needsProtoHack.has(baseProto)) {
-                    newObj = new proto.constructor();
-                    if (proto !== baseProto) {
-                        Object.setPrototypeOf(newObj, proto);
-                    }
-                }
-                else {
-                    newObj = Object.create(proto);
-                }
-            }
-            else if (internals.needsProtoHack.has(baseProto)) {
-                newObj = new baseProto.constructor();
-            }
-            else {
-                newObj = {};
-            }
+    if (baseProto === Types.buffer) {
+        return Buffer && Buffer.from(obj);              // $lab:coverage:ignore$
+    }
+
+    if (baseProto === Types.date) {
+        return new Date(obj.getTime());
+    }
+
+    if (baseProto === Types.regex) {
+        return new RegExp(obj);
+    }
+
+    // Generic objects
+
+    const newObj = internals.base(obj, baseProto, options);
+    if (newObj === obj) {
+        return obj;
     }
 
     if (seen) {
@@ -96,35 +74,38 @@ module.exports = internals.clone = function (obj, options = {}, _seen = null) {
     }
 
     const keys = Utils.keys(obj, options);
-    for (let i = 0; i < keys.length; ++i) {
-        const key = keys[i];
-
+    for (const key of keys) {
         if (baseProto === Types.array &&
             key === 'length') {
 
+            newObj.length = obj.length;
             continue;
         }
 
         const descriptor = Object.getOwnPropertyDescriptor(obj, key);
-        if (descriptor &&
-            (descriptor.get || descriptor.set)) {
+        if (descriptor) {
+            if (descriptor.get ||
+                descriptor.set) {
 
-            Object.defineProperty(newObj, key, descriptor);
+                Object.defineProperty(newObj, key, descriptor);
+            }
+            else if (descriptor.enumerable) {
+                newObj[key] = clone(obj[key], options, seen);
+            }
+            else {
+                Object.defineProperty(newObj, key, { enumerable: false, writable: true, configurable: true, value: clone(obj[key], options, seen) });
+            }
         }
         else {
             Object.defineProperty(newObj, key, {
-                enumerable: descriptor ? descriptor.enumerable : true,
+                enumerable: true,
                 writable: true,
                 configurable: true,
                 value: clone(obj[key], options, seen)
             });
         }
     }
 
-    if (baseProto === Types.array) {
-        newObj.length = obj.length;
-    }
-
     return newObj;
 };
 
@@ -140,3 +121,37 @@ internals.cloneWithShallow = function (source, options) {
     Utils.restore(copy, source, storage);         // Shallow copy the stored items and restore
     return copy;
 };
+
+
+internals.base = function (obj, baseProto, options) {
+
+    if (baseProto === Types.array) {
+        return [];
+    }
+
+    if (options.prototype === false) {                  // Defaults to true
+        if (internals.needsProtoHack.has(baseProto)) {
+            return new baseProto.constructor();
+        }
+
+        return {};
+    }
+
+    const proto = Object.getPrototypeOf(obj);
+    if (proto &&
+        proto.isImmutable) {
+
+        return obj;
+    }
+
+    if (internals.needsProtoHack.has(baseProto)) {
+        const newObj = new proto.constructor();
+        if (proto !== baseProto) {
+            Object.setPrototypeOf(newObj, proto);
+        }
+
+        return newObj;
+    }
+
+    return Object.create(proto);
+};