Does XSJS Support the |= bit wise OR operator?

I am trying to build a sha1 hash function and I need low level big endian functionality.

Currently I'm looking at the following error:

Found the following errors:

===========================

ReferenceError: reference to undefined property x[(len >> 5)]

Here is my line of code:

  x[len >> 5] |= 0x80 << (24 - len % 32);

At first I thought it was the shift operator << but I have them elsewhere and it doesn't seem to be erroring out.

Any ideas?