encode/decode base64 with JS

Encoding to base64 is done with the btoa command

btoa("This is a test.")
> "VGhpcyBpcyBhIHRlc3Qu"

To decode a base64 encoded string, use the atob command

atob("VGhpcyBpcyBhIHRlc3Qu")
> "This is a test."

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