Chrome ver. 79.0
Confirmation of operation with console of Dev tool
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."