chunks of an Uint8Array

As I'd said above, Chrome is spec compliant. See: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array

The constructor is:

new Uint8Array(length);
new Uint8Array(typedArray);
new Uint8Array(object);
new Uint8Array(buffer [, byteOffset [, length]]);

In this case, you're not passing in buffer, but typedArray - so the next 2 arguments are not being used. If you instead so (new Uint8Array(b.buffer,0,5)).length it'll work