Treat ArrayBuffers from another context as valid

Fixes: https://github.com/feross/buffer/issues/166
ArrayBuffers from another context (i.e. an iframe) do not pass the
`instanceof` check but they should be treated as valid.

diff --git a/index.js b/index.js
index b62b110b3061f270be1c1c8c325b029e989cbdda..f696940e7c3e3db74ab120a08794fcdb40abbec5 100644 (file)
--- a/index.js
+++ b/index.js
@@ -104,7 +104,7 @@ function from (value, encodingOrOffset, length) {
     throw new TypeError('"value" argument must not be a number')
   }
 
-  if (value instanceof ArrayBuffer) {
+  if (isArrayBuffer(value)) {
     return fromArrayBuffer(value, encodingOrOffset, length)
   }
 
@@ -364,7 +364,7 @@ function byteLength (string, encoding) {
   if (Buffer.isBuffer(string)) {
     return string.length
   }
-  if (isArrayBufferView(string) || string instanceof ArrayBuffer) {
+  if (isArrayBufferView(string) || isArrayBuffer(string)) {
     return string.byteLength
   }
   if (typeof string !== 'string') {
@@ -1696,6 +1696,14 @@ function blitBuffer (src, dst, offset, length) {
   return i
 }
 
+// ArrayBuffers from another context (i.e. an iframe) do not pass the `instanceof` check
+// but they should be treated as valid. See: https://github.com/feross/buffer/issues/166
+function isArrayBuffer (obj) {
+  return obj instanceof ArrayBuffer ||
+    (obj != null && obj.constructor != null && obj.constructor.name === 'ArrayBuffer' &&
+      typeof obj.byteLength === 'number')
+}
+
 // Node 0.10 supports `ArrayBuffer` but lacks `ArrayBuffer.isView`
 function isArrayBufferView (obj) {
   return (typeof ArrayBuffer.isView === 'function') && ArrayBuffer.isView(obj)