How to convert uint8 Array to base64 Encoded String?

Question

I got a webSocket comunication, I recieve base64 encoded string, convert it to uint8 and work on it, but now I need to send back, I got the uint8 array, and need to convert it to base64 string, so I can send it. How can I make this convertion?

Answer 1

If your data may contain multi-byte sequences (not a plain ASCII sequence) and your browser has TextDecoder, then you should use that to decode your data (specify the required encoding for the TextDecoder):

var u8 = new Uint8Array([65, 66, 67, 68]); var decoder = new TextDecoder('utf8'); var b64encoded = btoa(decoder.decode(u8)); 

If you need to support browsers that do not have TextDecoder (currently just IE and Edge), then the best option is to use a TextDecoder polyfill.

If your data contains plain ASCII (not multibyte Unicode/UTF-8) then there is a simple alternative using String.fromCharCode that should be fairly universally supported:

var ascii = new Uint8Array([65, 66, 67, 68]); var b64encoded = btoa(String.fromCharCode.apply(null, ascii)); 

And to decode the base64 string back to a Uint8Array:

var u8_2 = new Uint8Array(atob(b64encoded).split("").map(function(c) {     return c.charCodeAt(0); })); 

If you have very large array buffers then the apply may fail and you may need to chunk the buffer (based on the one posted by @RohitSengar). Again, note that this is only correct if your buffer only contains non-multibyte ASCII characters:

function Uint8ToString(u8a){   var CHUNK_SZ = 0x8000;   var c = [];   for (var i=0; i < u8a.length; i+=CHUNK_SZ) {     c.push(String.fromCharCode.apply(null, u8a.subarray(i, i+CHUNK_SZ)));   }   return c.join(""); } // Usage var u8 = new Uint8Array([65, 66, 67, 68]); var b64encoded = btoa(Uint8ToString(u8));