So, I got around to it and I tested my lib on nodejs.
Your first example (using Base64String.compress) cannot work as Base64String is meant to compress base64 encoded content. Your string ("This is my compression test.") is not a valid base64 string. So it doesn't work. Basically Base64String is meant to reencode Base64 content (usually images). The rationale is that base64 takes up a full character to store 6 bits, while compressToUTF16 stores 15 bits per characters.
Your second example is more useful in that really, it doesn't work. It looks as if your compressed test string triggers a bug in either compressToUTF16 or decompressToUTF16. I'm working on it as soon as I get home.
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