Base64 encoding of String in Node.js

I try to encode a string in both browser and server but I have different base64 encoding for a specific string

Here is my string: "£aº©S=³hPó c¨¸" (Hexa: 00a3006100ba00a900940053003d00b30068005000f300900020006300a800b8 )

Client-side: I encode this String using btoa() and I have : o2G6qZRTPbNoUPOQIGOouA== and this is the result I expect.

Server-side: I code this String using Buffer according to this answer in Node.js i have :

var ciphertext = ... // myString
console.log(ciphertext.hexEncode()); // 00a3006100ba00a900940053003d00b30068005000f300900020006300a800b8  
console.log(Buffer.from(ciphertext, 'utf8').toString('base64')) // wqNhwrrCqcKUUz3Cs2hQw7PCkCBjwqjCuA==
console.log(Buffer.from(ciphertext, 'ucs2').toString('base64')) // owBhALoAqQCUAFMAPQCzAGgAUADzAJAAIABjAKgAuAA=

via Zycho