Fixes & optimizations to es6.spec.arrowFunctions.

src/babel/transformation/templates/helper-new-arrow-check.js

@@ -1,5 +1,5 @@
-(function (instance, arrowFn) {
-  if (instance instanceof arrowFn) {
+(function (innerThis, boundThis) {
+  if (innerThis !== boundThis) {
     throw new TypeError("Cannot instantiate an arrow function");
   }
 });

src/babel/transformation/transformers/es6/spec.arrow-functions.js

@@ -8,19 +8,14 @@ export function ArrowFunctionExpression(node, parent, scope, file) {
   if (node.shadow) return;
   node.shadow = { this: false };
 
-  var {id} = node;
-  var expr = node;
-
-  if (!id) {
-    id = scope.parent.generateDeclaredUidIdentifier("arrow");
-    expr = t.assignmentExpression("=", id, expr);
-  }
+  var boundThis = t.thisExpression();
+  boundThis._shadowedFunctionLiteral = false;
 
   // make sure that arrow function won't be instantiated
   t.ensureBlock(node).body.unshift(t.expressionStatement(t.callExpression(file.addHelper("new-arrow-check"), [
     t.thisExpression(),
-    id
+    boundThis
   ])));
 
-  return t.callExpression(t.memberExpression(expr, t.identifier("bind")), [t.thisExpression()]);
+  return t.callExpression(t.memberExpression(node, t.identifier("bind")), [t.thisExpression()]);
 }

src/babel/transformation/transformers/internal/shadow-functions.js

@@ -23,13 +23,11 @@ function remap(path, key, create) {
 }
 
 export function ThisExpression(node) {
-  if (!node._shadowedFunctionLiteral) {
-    return remap(this, "this", () => t.thisExpression());
-  }
+  return remap(this, "this", () => t.thisExpression());
 }
 
 export function ReferencedIdentifier(node) {
-  if (node.name === "arguments" && !node._shadowedFunctionLiteral) {
+  if (node.name === "arguments") {
     return remap(this, "arguments", () => t.identifier("arguments"));
   }
 }

src/babel/traversal/path/ancestry.js

@@ -64,9 +64,13 @@ export function inType(types) {
 
 export function inShadow(key) {
   var path = this;
+  var dontShadow = path.node._shadowedFunctionLiteral;
+  if (dontShadow !== undefined) {
+    return !dontShadow;
+  }
   while (path) {
     if (path.isFunction()) {
-      var {shadow} = path.node;
+      var { shadow } = path.node;
       if (shadow && (shadow === true || shadow[key] !== false)) {
         return path;
       } else {

test/core/fixtures/transformation/es6.arrow-functions/spec/expected.js

@@ -1,25 +1,20 @@
 "use strict";
 
-var _arrow;
-
-function _newArrowCheck(instance, arrowFn) { if (instance instanceof arrowFn) { throw new TypeError("Cannot instantiate an arrow function"); } }
-
-arr.map((_arrow = function (x) {
-  _newArrowCheck(this, _arrow);
+var _this = this;
 
+arr.map((function (x) {
+  babelHelpers.newArrowCheck(this, _this);
   return x * x;
 }).bind(this));
 var f = (function f(x, y) {
-  _newArrowCheck(this, f);
-
+  babelHelpers.newArrowCheck(this, _this);
   return x * y;
 }).bind(this);
 (function () {
-  var _arrow2;
-
-  return (_arrow2 = function () {
-    _newArrowCheck(this, _arrow2);
+  var _this2 = this;
 
+  return (function () {
+    babelHelpers.newArrowCheck(this, _this2);
     return this;
   }).bind(this);
 })();

test/core/fixtures/transformation/es6.arrow-functions/spec/options.json

@@ -1,3 +1,4 @@
 {
+  "externalHelpers": true,
 	"optional": ["es6.spec.arrowFunctions"]
 }