remap UpdateExpression in module exports - closes #334

lib/6to5/transformation/modules/_default.js

@@ -44,16 +44,42 @@ DefaultFormatter.prototype.remapAssignments = function () {
   var self = this;
 
   var isLocalReference = function (node, scope) {
-    var left = node.left;
-    var name = left.name;
-    return t.isIdentifier(left) && localExports[name] && localExports[name] === scope.get(name, true);
+    var name = node.name;
+    return t.isIdentifier(node) && localExports[name] && localExports[name] === scope.get(name, true);
   };
 
   traverse(this.file.ast, {
     enter: function (node, parent, scope) {
-      if (t.isExportDeclaration(node)) return false;
+      if (t.isUpdateExpression(node) && isLocalReference(node.argument, scope)) {
+        this.stop();
 
-      if (t.isAssignmentExpression(node) && isLocalReference(node, scope)) {
+        // expand to long file assignment expression
+        var assign = t.assignmentExpression(node.operator[0] + "=", node.argument, t.literal(1));
+
+        // remap this assignment expression
+        var remapped = self.remapExportAssignment(assign);
+
+        // we don't need to change the result
+        if (t.isExpressionStatement(parent) || node.prefix) {
+          return remapped;
+        }
+
+        var nodes = [];
+        nodes.push(remapped);
+
+        var operator;
+        if (node.operator === "--") {
+          operator = "+";
+        } else { // "++"
+          operator = "-";
+        }
+        nodes.push(t.binaryExpression(operator, node.argument, t.literal(1)));
+
+        return t.sequenceExpression(nodes);
+      }
+
+      if (t.isAssignmentExpression(node) && isLocalReference(node.left, scope)) {
+        this.stop();
         return self.remapExportAssignment(node);
       }
     }

lib/6to5/transformation/modules/amd.js

@@ -6,7 +6,7 @@ var t                = require("../../types");
 var _                = require("lodash");
 
 function AMDFormatter(file) {
-  this.file = file;
+  DefaultFormatter.apply(this, arguments);
   this.ids  = {};
 }
 

lib/6to5/transformation/modules/system.js

@@ -7,10 +7,11 @@ var t                = require("../../types");
 var _                = require("lodash");
 
 function SystemFormatter(file) {
+  this.exportIdentifier  = file.generateUidIdentifier("export");
+
   AMDFormatter.apply(this, arguments);
 
   this.moduleNameLiteral = t.literal(this.getModuleName());
-  this.exportIdentifier  = file.generateUidIdentifier("export");
 }
 
 util.inherits(SystemFormatter, AMDFormatter);