header order

lib/po.js

@@ -8,6 +8,7 @@ var PO = function () {
     this.comments = [];
     this.extractedComments = [];
     this.headers = {};
+    this.headerOrder = [];
     this.items = [];
 };
 
@@ -32,9 +33,24 @@ PO.prototype.toString = function () {
     lines.push('msgid ""');
     lines.push('msgstr ""');
 
-    var keys = Object.keys(this.headers);
     var self = this;
+    var headerOrder = [];
+
+    this.headerOrder.forEach(function (key) {
+        if (key in self.headers) {
+            headerOrder.push(key);
+        }
+    });
+
+    var keys = Object.keys(this.headers);
+
     keys.forEach(function (key) {
+        if (headerOrder.indexOf(key) === -1) {
+            headerOrder.push(key);
+        }
+    });
+
+    headerOrder.forEach(function (key) {
         lines.push('"' + key + ': ' + self.headers[key] + '\\n"');
     });
 
@@ -88,6 +104,7 @@ PO.parse = function (data) {
         'Content-Transfer-Encoding': '',
         'Plural-Forms': '',
     };
+    po.headerOrder = [];
 
     headers.split(/\n/).reduce(function (acc, line) {
         if (acc.merge) {
@@ -111,6 +128,7 @@ PO.parse = function (data) {
             var name = p.shift().trim();
             var value = p.join(':').trim();
             po.headers[name] = value;
+            po.headerOrder.push(name);
         }
     });