Add more type validation to codec.js

mojo/public/js/codec.js

Index: mojo/public/js/codec.js
diff --git a/mojo/public/js/codec.js b/mojo/public/js/codec.js
index 5440abed92d3651e684a492f97673bee286d9d68..f071d2f870923c6cd2202f7a692b3a17d853c140 100644
--- a/mojo/public/js/codec.js
+++ b/mojo/public/js/codec.js
@@ -8,7 +8,9 @@ define("mojo/public/js/codec", [
 ], function(unicode, buffer) {
 
   var kErrorUnsigned = "Passing negative value to unsigned";
-  var kErrorArray = "Passing non-array-like to array";
+  var kErrorArray = "Passing non Array for array type";
+  var kErrorString = "Passing non String for string type";
+  var kErrorMap = "Passing non Map for map type";
 
   // Memory -------------------------------------------------------------------
 
@@ -353,7 +355,7 @@ define("mojo/public/js/codec", [
       this.encodePointer(val);
       return;
     }
-    if (val.length === undefined) {
+    if (!(val instanceof Array)) {
       throw new Error(kErrorArray);
     }

[Ryan Sleevi, 2014/12/30 04:54:17]

The original code had the benefit that it properly handled ES6 array-like
objects, such as the ArrayBufferView family. This change loses this property,
which has prevented rolling an updated Mojo into Chrome (see
https://codereview.chromium.org/795593004 )

This may be what you desired, but it's certainly not intuitive when using JS
bindings.

https://people.mozilla.org/~jorendorff/es6-draft.html#sec-createlistfromarray...
is the canonical ES6 algorithm for handling array-like objects into sequenced
lists, and it seems useful here when talking about IDL bindings.

     var numberOfElements = val.length;
@@ -369,6 +371,10 @@ define("mojo/public/js/codec", [
       this.encodePointer(val);
       return;
     }
+    // This only accepts string literals, not objects like new String("foo").
+    if (typeof(val) !== "string") {
+      throw new Error(kErrorString);
+    }
     var encodedSize = kArrayHeaderSize + unicode.utf8Length(val);
     var encoder = this.createAndEncodeEncoder(encodedSize);
     encoder.encodeString(val);
@@ -394,6 +400,9 @@ define("mojo/public/js/codec", [
       this.encodePointer(val);
       return;
     }
+    if (!(val instanceof Map)) {

[Ryan Sleevi, 2014/12/30 04:54:17]

This is another surprising change, as it prevents map-like objects and iterables
from working. Again, this may be desirable, but it certainly strikes as
surprising.

+      throw new Error(kErrorMap);
+    }
     var encodedSize = kStructHeaderSize + kMapStructPayloadSize;
     var encoder = this.createAndEncodeEncoder(encodedSize);
     encoder.encodeMap(keyClass, valueClass, val);