fix(ejson-serialize): prevent double serialization for nested documents

* don't require mongodb on browser tests

(part of the fix to #303)

* Revert "don't require mongodb on browser tests"

This reverts commit 3dc2cc1.

* Remove double serialization of nested docs

* combined two lines per code review

lib/extended_json.js

@@ -251,53 +251,44 @@ function serializeValue(value, options) {
     return { $numberDouble: value.toString() };
   }
 
+  if (value instanceof RegExp) {
+    let flags = value.flags;
+    if (flags === undefined) {
+      flags = value.toString().match(/[gimuy]*$/)[0];
+    }
+
+    const rx = new BSONRegExp(value.source, flags);
+    return rx.toExtendedJSON();
+  }
+
   if (value != null && typeof value === 'object') return serializeDocument(value, options);
   return value;
 }
 
 function serializeDocument(doc, options) {
   if (doc == null || typeof doc !== 'object') throw new Error('not an object instance');
 
-  // the document itself is a BSON type
-  if (doc._bsontype && typeof doc.toExtendedJSON === 'function') {
-    if (doc._bsontype === 'Code' && doc.scope) {
-      doc.scope = serializeDocument(doc.scope, options);
-    } else if (doc._bsontype === 'DBRef' && doc.oid) {
-      doc.oid = serializeDocument(doc.oid, options);
-    }
-
-    return doc.toExtendedJSON(options);
-  }
-
-  // the document is an object with nested BSON types
-  const _doc = {};
-  for (let name in doc) {
-    let val = doc[name];
-    if (Array.isArray(val)) {
-      _doc[name] = serializeArray(val, options);
-    } else if (val != null && typeof val.toExtendedJSON === 'function') {
-      if (val._bsontype === 'Code' && val.scope) {
-        val.scope = serializeDocument(val.scope, options);
-      } else if (val._bsontype === 'DBRef' && val.oid) {
-        val.oid = serializeDocument(val.oid, options);
+  // the "document" is a BSON type
+  if (doc._bsontype) {
+    if (typeof doc.toExtendedJSON === 'function') {
+      // TODO: the two cases below mutate the original document! Bad.  I don't know
+      // enough about these two BSON types to know how to safely clone these objects, but
+      // someone who knows MongoDB better should fix this to clone instead of mutating input objects.
+      if (doc._bsontype === 'Code' && doc.scope) {
+        doc.scope = serializeDocument(doc.scope, options);
+      } else if (doc._bsontype === 'DBRef' && doc.oid) {
+        doc.oid = serializeDocument(doc.oid, options);
       }
 
-      _doc[name] = val.toExtendedJSON(options);
-    } else if (val instanceof Date) {
-      _doc[name] = serializeValue(val, options);
-    } else if (val != null && typeof val === 'object') {
-      _doc[name] = serializeDocument(val, options);
+      return doc.toExtendedJSON(options);
     }
-    _doc[name] = serializeValue(val, options);
-    if (val instanceof RegExp) {
-      let flags = val.flags;
-      if (flags === undefined) {
-        flags = val.toString().match(/[gimuy]*$/)[0];
-      }
+    // TODO: should we throw an exception if there's a BSON type that has no toExtendedJSON method?
+  } 
 
-      const rx = new BSONRegExp(val.source, flags);
-      _doc[name] = rx.toExtendedJSON();
-    }
+  // Recursively serialize this document's property values. 
+  const _doc = {};
+  for (let name in doc) {
+    _doc[name] = serializeValue(doc[name], options);
   }
 
   return _doc;