String.prototype[Symbol.iterator] does RequireObjectCoercible(this)

src/js/string-iterator.js

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 (function(global, utils) {
 
 "use strict";
 
 %CheckIsBootstrapping();
 
@@ skipping 14 matching lines @@
   MakeTypeError = from.MakeTypeError;
 });
 
 // -------------------------------------------------------------------
 
 function StringIterator() {}
 
 
 // 21.1.5.1 CreateStringIterator Abstract Operation
 function CreateStringIterator(string) {
+  if (IS_NULL_OR_UNDEFINED(string)) {

[adamk, 2016/03/09 23:31:58]

There's a macro for this:

CHECK_OBJECT_COERCIBLE(string, 'String.prototype[Symbol.iterator]');

[Dan Ehrenberg, 2016/03/09 23:53:59]

Awesome, applied

+    throw MakeTypeError(kIncompatibleMethodReceiver,
+                        'String.prototype[Symbol.iterator]');
+  }
   var s = TO_STRING(string);
   var iterator = new StringIterator;
   SET_PRIVATE(iterator, stringIteratorIteratedStringSymbol, s);
   SET_PRIVATE(iterator, stringIteratorNextIndexSymbol, 0);
   return iterator;
 }
 
 
 // ES6 section 21.1.5.2.1 %StringIteratorPrototype%.next ( )
 function StringIteratorNext() {
@@ skipping 48 matching lines @@
   'next', StringIteratorNext
 ]);
 %AddNamedProperty(StringIterator.prototype, toStringTagSymbol,
                   "String Iterator", READ_ONLY | DONT_ENUM);
 
 utils.SetFunctionName(StringPrototypeIterator, iteratorSymbol);
 %AddNamedProperty(GlobalString.prototype, iteratorSymbol,
                   StringPrototypeIterator, DONT_ENUM);
 
 })