Question

According to MSDN I can create a Uint32Array in 3 ways:

1. new Uint32Array( length );
2. new Uint32Array( array );
3. new Uint32Array( buffer, byteOffset, length );

First and second method work great, but third didn’t work for me. What’s wrong in this code?

var buffer = new ArrayBuffer(8);
var uint32s = new Uint32Array(buffer, 4, 4);
uint32s[0] = 0x05050505;
var uint8s = new Uint8Array(buffer);
for (var i =0; i< 8; i++)
{
    alert(uint8s[i]);
}

This works fine, but of course byteOffset = 0.

var uint32s = new Uint32Array(buffer);

Answer 1

It seems that the documentation is incorrect here in that length is not a number of bytes but the number of 32-bit integers that the Uint32Array will contain.

Exhibit A

Changing the code to var uint32s = new Uint32Array(buffer, 4, 1); works.

Exhibit B

The documentation for Uint32Array on MDN says that length is a count of items, not bytes.

Exhibit C

It doesn’t really make sense to have the constructor accept a length in bytes. What should happen if length is not a multiple of 4?