Why were Javascript atob and btoa named like that

Question

A base64 string and window are both decoded using Javascript's window.atob() function.

A string is base64 encoded using the btoa() function.

If that is the case, why weren't they given names like base64Decode() and base64Encode()?

The functions atob() and btoa() are completely nonsemantic, hence they are useless.

 

I am curious as to why.