v2.13.1

CHANGELOG.md

@@ -11,6 +11,11 @@
 
 _Note: Gaps between patch versions are faulty/broken releases._
 
+## 2.13.1
+
+ * **New Feature**
+  * Temporal dead zone for block binding.
+
 ## 2.13.0
 
  * **New Feature**

lib/6to5/transformation/transformers/es6-let-scoping.js

@@ -57,6 +57,7 @@ exports.Loop = function (node, parent, scope, context, file) {
   }
 };
 
+exports.Program =
 exports.BlockStatement = function (block, parent, scope, context, file) {
   if (!t.isLoop(parent)) {
     var letScoping = new LetScoping(false, block, parent, scope, file);
@@ -82,6 +83,7 @@ function LetScoping(loopParent, block, parent, scope, file) {
   this.file       = file;
 
   this.outsideLetReferences = {};
+  this.hasLetReferences     = false;
   this.letReferences        = {};
   this.body                 = [];
 }
@@ -95,10 +97,15 @@ LetScoping.prototype.run = function () {
   if (block._letDone) return;
   block._letDone = true;
 
-  // this is a block within a `Function` so we can safely leave it be
-  if (t.isFunction(this.parent)) return;
-
   var needsClosure = this.getLetReferences();
+  this.checkTDZ();
+
+  // this is a block within a `Function/Program` so we can safely leave it be
+  if (t.isFunction(this.parent) || t.isProgram(this.block)) return;
+
+  // we can skip everything
+  if (!this.hasLetReferences) return;
+
   if (needsClosure) {
     this.needsClosure();
   } else {
@@ -106,6 +113,48 @@ LetScoping.prototype.run = function () {
   }
 };
 
+/**
+ * Description
+ */
+
+LetScoping.prototype.checkTDZ = function () {
+  var state = {
+    letRefs: this.letReferences,
+    file: this.file
+  };
+
+  traverse(this.block, {
+    enter: function (node, parent, scope, context, state) {
+      if (!t.isIdentifier(node)) return;
+      if (!t.isReferenced(node, parent)) return;
+
+      var declared = state.letRefs[node.name];
+      if (!declared) return;
+
+      // declared node is different in this scope
+      if (scope.get(node.name, true) !== declared) return;
+
+      var declaredLoc  = declared.loc;
+      var referenceLoc = node.loc;
+
+      if (!declaredLoc || !referenceLoc) return;
+
+      // does this reference appear on a line before the declaration?
+      var before = referenceLoc.start.line < declaredLoc.start.line;
+
+      if (referenceLoc.start.line === declaredLoc.start.line) {
+        // this reference appears on the same line
+        // check it appears before the declaration
+        before = referenceLoc.start.col < declaredLoc.start.col;
+      }
+
+      if (before) {
+        throw state.file.errorWithNode(node, "Temporal dead zone - accessing a variable before it's initialized");
+      }
+    }
+  }, this.scope, state);
+};
+
 /**
  * Description
  */
@@ -239,8 +288,12 @@ LetScoping.prototype.getLetReferences = function () {
     declar = declarators[i];
     var keys = t.getIds(declar, true);
     _.extend(this.letReferences, keys);
+    this.hasLetReferences = true;
   }
 
+  // no let references so we can just quit
+  if (!this.hasLetReferences) return;
+
   // set let references to plain var references
   standardiseLets(declarators);
 

lib/6to5/transformation/transformers/spec-block-scoped-functions.js

@@ -7,6 +7,9 @@ exports.FunctionDeclaration = function (node, parent) {
     return;
   }
 
+  // this is to avoid triggering the TDZ detection
+  node.id.loc = null;
+
   var declar = t.variableDeclaration("let", [
     t.variableDeclarator(node.id, t.toExpression(node))
   ]);

package.json

@@ -1,7 +1,7 @@
 {
   "name": "6to5",
   "description": "Turn ES6 code into readable vanilla ES5 with source maps",
-  "version": "2.13.0",
+  "version": "2.13.1",
   "author": "Sebastian McKenzie <sebmck@gmail.com>",
   "homepage": "https://6to5.org/",
   "repository": "6to5/6to5",

test/fixtures/transformation/es6-let-scoping/temporal-dead-zone/actual.js

@@ -0,0 +1,2 @@
+qux;
+let qux = 456;

test/fixtures/transformation/es6-let-scoping/temporal-dead-zone/options.json

@@ -0,0 +1,3 @@
+{
+  "throws": "Temporal dead zone - accessing a variable before it's initialized"
+}