diff --git a/lib/6to5/file.js b/lib/6to5/file.js
index b42aac76ee..a74d1daa4b 100644
--- a/lib/6to5/file.js
+++ b/lib/6to5/file.js
@@ -2,13 +2,12 @@ module.exports = File;
 
 var SHEBANG_REGEX = /^\#\!.*/;
 
-var Transformer = require("./transformation/transformer");
-var transform   = require("./transformation/transform");
-var generate    = require("./generation/generator");
-var Scope       = require("./traverse/scope");
-var util        = require("./util");
-var t           = require("./types");
-var _           = require("lodash");
+var transform = require("./transformation/transform");
+var generate  = require("./generation/generator");
+var Scope     = require("./traverse/scope");
+var util      = require("./util");
+var t         = require("./types");
+var _         = require("lodash");
 
 function File(opts) {
   this.opts = File.normaliseOptions(opts);
diff --git a/lib/6to5/transformation/modules/_default.js b/lib/6to5/transformation/modules/_default.js
index e98efcb641..e4fedc0b48 100644
--- a/lib/6to5/transformation/modules/_default.js
+++ b/lib/6to5/transformation/modules/_default.js
@@ -43,10 +43,6 @@ DefaultFormatter.prototype.remapAssignments = function () {
   var localExports = this.localExports;
   var self = this;
 
-  var throwIllegal = function (node) {
-    // todo!!
-  };
-
   var isLocalReference = function (node, scope) {
     var left = node.left;
     var name = left.name;
@@ -111,8 +107,6 @@ DefaultFormatter.prototype._hoistExport = function (declar, assign) {
 };
 
 DefaultFormatter.prototype._exportSpecifier = function (getRef, specifier, node, nodes) {
-  var variableName = t.getSpecifierName(specifier);
-
   var inherits = false;
   if (node.specifiers.length === 1) inherits = node;
 
@@ -163,7 +157,7 @@ DefaultFormatter.prototype.exportDeclaration = function (node, nodes) {
         decl.init = this._exportsAssign(decl.id, decl.init).expression;
 
         var newDeclar = t.variableDeclaration(declar.kind, [decl]);
-        if (i == 0) t.inherits(newDeclar, declar);
+        if (i === "0") t.inherits(newDeclar, declar);
         nodes.push(newDeclar);
       }
     } else {
diff --git a/lib/6to5/transformation/modules/system.js b/lib/6to5/transformation/modules/system.js
index ae1402c651..3358599e57 100644
--- a/lib/6to5/transformation/modules/system.js
+++ b/lib/6to5/transformation/modules/system.js
@@ -2,15 +2,10 @@ module.exports = SystemFormatter;
 
 var DefaultFormatter = require("./_default");
 var AMDFormatter     = require("./amd");
-var traverse         = require("../../traverse");
 var util             = require("../../util");
 var t                = require("../../types");
 var _                = require("lodash");
 
-var SETTER_MODULE_NAMESPACE        = t.identifier("m");
-var PRIVATE_MODULE_NAME_IDENTIFIER = t.identifier("__moduleName");
-var NULL_SETTER                    = t.literal(null);
-
 function SystemFormatter(file) {
   AMDFormatter.apply(this, arguments);
 
@@ -39,7 +34,7 @@ SystemFormatter.prototype._exportsWildcard = function (objectIdentifier) {
   return t.forInStatement(left, right, block);
 };
 
-SystemFormatter.prototype._exportsAssign = function (id, init, isExpression) {
+SystemFormatter.prototype._exportsAssign = function (id, init) {
   return this.buildExportCall(t.literal(id.name), init, true);
 };
 
diff --git a/lib/6to5/transformation/transformers/react.js b/lib/6to5/transformation/transformers/react.js
index 0f1de5be78..50895a6e95 100644
--- a/lib/6to5/transformation/transformers/react.js
+++ b/lib/6to5/transformation/transformers/react.js
@@ -115,8 +115,8 @@ exports.XJSElement = {
         for (i in lines) {
           var line = lines[i];
 
-          var isFirstLine = i == 0;
-          var isLastLine = i == lines.length - 1;
+          var isFirstLine = i === "0";
+          var isLastLine = +i === lines.length - 1;
 
           // replace rendered whitespace tabs with spaces
           var trimmedLine = line.replace(/\t/g, ' ');