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

lib/6to5/file.js

@@ -9,6 +9,7 @@ var transform  = require("./transformation");
 var generate   = require("./generation");
 var defaults   = require("lodash/object/defaults");
 var contains   = require("lodash/collection/contains");
+var traverse   = require("./traverse");
 var clone      = require("./helpers/clone");
 var Scope      = require("./traverse/scope");
 var util       = require("./util");
@@ -352,6 +353,8 @@ File.prototype.transform = function (ast) {
     modFormatter.init();
   }
 
+  this.checkNode(ast);
+
   var astRun = function (key) {
     each(self.transformerStack, function (pass) {
       pass.astRun(key);
@@ -367,6 +370,30 @@ File.prototype.transform = function (ast) {
   astRun("exit");
 };
 
+var checkTransformerVisitor = {
+  enter: function (node, parent, scope, context, state) {
+    state.check(node, scope);
+  }
+};
+
+File.prototype.checkNode = function (node, scope) {
+  var self = this;
+  scope = scope || this.scope;
+
+  var check = function (node, scope) {
+    each(self.transformerStack, function (pass) {
+      if (pass.shouldRun) return;
+      pass.checkNode(node, scope);
+    });
+  };
+
+  check(node, scope);
+
+  traverse(node, checkTransformerVisitor, scope, {
+    check: check
+  });
+};
+
 File.prototype.generate = function () {
   var opts = this.opts;
   var ast  = this.ast;