before scripts do not behave as expected when top-level document is not an array

[charles-dyfis-net]

Given a document that looks like so:

{ 'foo': [1,2,3,4] }

I would expect to be able to use a before script to replace the document with only the array, and have my jsawk script operate only on that array:

jsawk -b 'return this["foo"]' <<<"{'foo':[1,2,3,4]}"

However, this fails:

TypeError: IS has no properties

[cyberhuman]

For those curious how to do it:

jsawk -b 'return this[0].foo' -a 'return [this]' 'return this+1'