i made the javascripts faster with a transformer prepass to check what transformers actually have to be ran

lib/6to5/traverse/index.js

@@ -10,11 +10,12 @@ var contains = require("lodash/collection/contains");
 var flatten  = require("lodash/array/flatten");
 var compact  = require("lodash/array/compact");
 
-function TraversalContext() {
+function TraversalContext(scope) {
   this.shouldFlatten = false;
   this.shouldRemove  = false;
   this.shouldSkip    = false;
   this.shouldStop    = false;
+  this.scope         = scope;
 }
 
 TraversalContext.prototype.flatten = function () {
@@ -44,20 +45,31 @@ TraversalContext.prototype.reset = function () {
 TraversalContext.prototype.maybeRemove = function (obj, key) {
   if (this.shouldRemove) {
     obj[key] = null;
-    this.shouldFlatten = true;
+    this.flatten();
   }
 };
 
-function replaceNode(obj, key, node, result) {
-  var isArray = Array.isArray(result);
+TraversalContext.prototype.replaceNode = function (obj, key, node, replacement, scope) {
+  var isArray = Array.isArray(replacement);
 
   // inherit comments from original node to the first replacement node
-  var inheritTo = result;
-  if (isArray) inheritTo = result[0];
+  var inheritTo = replacement;
+  if (isArray) inheritTo = replacement[0];
   if (inheritTo) t.inheritsComments(inheritTo, node);
 
   // replace the node
-  obj[key] = result;
+  obj[key] = replacement;
+
+  var file = this.scope && this.scope.file;
+  if (file) {
+    if (isArray) {
+      for (var i = 0; i < replacement.length; i++) {
+        file.checkNode(replacement[i], scope);
+      }
+    } else {
+      file.checkNode(replacement, scope);
+    }
+  }
 
   // we're replacing a statement or block node with an array of statements so we better
   // ensure that it's a block
@@ -66,39 +78,16 @@ function replaceNode(obj, key, node, result) {
   }
 
   if (isArray) {
-    return true;
+    this.flatten();
   }
-}
-
-TraversalContext.prototype.enterNode = function (obj, key, node, enter, parent, scope, state) {
-  var result = enter(node, parent, scope, this, state);
-  var flatten = false;
-
-  if (result) {
-    flatten = replaceNode(obj, key, node, result);
-    node = result;
-
-    if (flatten) {
-      this.shouldFlatten = true;
-    }
-  }
-
-  this.maybeRemove(obj, key);
-
-  return node;
 };
 
-TraversalContext.prototype.exitNode = function (obj, key, node, exit, parent, scope, state) {
-  var result = exit(node, parent, scope, this, state);
-  var flatten = false;
+TraversalContext.prototype.call = function (fn, obj, key, node, parent, scope, state) {
+  var replacement = fn(node, parent, scope, this, state);
 
-  if (result) {
-    flatten = replaceNode(obj, key, node, result);
-    node = result;
-
-    if (flatten) {
-      this.shouldFlatten = true;
-    }
+  if (replacement) {
+    this.replaceNode(obj, key, node, replacement, scope);
+    node = replacement;
   }
 
   this.maybeRemove(obj, key);
@@ -122,7 +111,7 @@ TraversalContext.prototype.visitNode = function (obj, key, opts, scope, parent,
     ourScope = new Scope(node, parent, scope);
   }
 
-  node = this.enterNode(obj, key, node, opts.enter, parent, ourScope, state);
+  node = this.call(opts.enter, obj, key, node, parent, ourScope, state);
 
   if (this.shouldSkip) {
     return this.shouldStop;
@@ -136,7 +125,7 @@ TraversalContext.prototype.visitNode = function (obj, key, opts, scope, parent,
     }
   } else {
     traverseNode(node, opts, ourScope, state);
-    this.exitNode(obj, key, node, opts.exit, parent, ourScope, state);
+    this.call(opts.exit, obj, key, node, parent, ourScope, state);
   }
 
   return this.shouldStop;
@@ -174,7 +163,7 @@ function traverseNode(node, opts, scope, state) {
   var keys = t.VISITOR_KEYS[node.type];
   if (!keys) return;
 
-  var context = new TraversalContext();
+  var context = new TraversalContext(scope);
   for (var i = 0; i < keys.length; i++) {
     if (context.visit(node, keys[i], opts, scope, state)) {
       return;

lib/6to5/traverse/scope.js

@@ -35,6 +35,18 @@ function Scope(block, parentBlock, parent, file) {
 
 Scope.defaultDeclarations = flatten([globals.builtin, globals.browser, globals.node].map(Object.keys));
 
+/**
+ * Description
+ *
+ * @param {Object} node
+ * @param {Object} opts
+ * @param [state]
+ */
+
+Scope.prototype.traverse = function (node, opts, state) {
+  traverse(node, opts, this, state);
+};
+
 /**
  * Description
  *