Kata description is a bit misleading. It should be mentioned, that the main object object's properties may also be objects (nesting!). At first I thought there would be no nesting. Moreover you should add an example.

Nailed it.
Bitwise operations in JS is something ... interesting :)
Thanks for your help!

Hmm... then how do you know if binary data encoding passed?
I mean all binary data encoding tests pass but the first binary data decoding fails.

Nice kata. Mentioning bit order would be a +

Here's another one:
Input: <~kYm=TbHJQ&Dr/./J,WWbK=]f9...~>
My result: [232, 83, 137, 109, 203, 175, 188, 34, 111, 222, 188, 173, 127, 254, 90, 189, 131, 186, 219, 83]
Expected: [232, 83, 137, 109, 203, 175, 188, 34, 111, 222, 188, 173, 128, 32, 170, 5, 59, 219, 189, 56]

You did a great job by adding a whole lot of unit tests.
I managed to get my code working with all the tests except for "Random binary string" ones.
The e6Blf part is the begging of input string from one of those failing tests.

I'm struggling to decode random binary data.
When I get <~e6Blf~> to decode my result is a string of chars [212, 91, 196, 250].
But test expects my result to be [212, 91, 197, 32].
How come? Any hints?

Description is a bit vague and I had to read discussions to learn that I have to return object