base64 encode/decode: btoa() and nodejs Buffer work different way?

in nodejs terminal:

> var s = String.fromCharCode(0x00,0x2B,0x20,0xFC);
> var t = new Buffer(s).toString('base64');
> console.log(s);
+ ü
> console.log(t);
ACsgw7w=
> 

string is String.fromCharCode(0x00,0x2B,0x20,0xFC) , the base64 string is "ACsgw7w="

and in Espruino Web IDE left-hand terminal:

>var s = String.fromCharCode(0x00,0x2B,0x20,0xFC);
="\x00+ \xFC"
>var t = btoa(s);
="ACsg/A=="

string is String.fromCharCode(0x00,0x2B,0x20,0xFC) , the base64 string is "ACsg/A=="

Why the same string gets different base64 encoded string in Espruino and nodejs?

The problem is actually with your node.js code :) If you look at what's in your buffer:

> var s = String.fromCharCode(0x00,0x2B,0x20,0xFC);
undefined
> var b = new Buffer(s);
undefined
> b
<Buffer 00 2b 20 c3 bc>
> b.length
5

You'll see that it's magically turned the string into a 5 byte buffer. Most likely it's because it is interpreting your string as a UTF8 string, when I guess you intended to use it just as a string of bytes.

Yes.
Just use 'ascii' to set the encoding format.

Thanks a lot.

> var s = String.fromCharCode(0x00,0x2B,0x20,0xFC);
undefined
> var b = new Buffer(s,'ascii');
undefined
> b
<Buffer 00 2b 20 fc>
> b.length
4
> b.toString('base64');
'ACsg/A=='