How to save a binary string to a file?

Question

Node.js

Good afternoon!
I get a binary file, convert it to a string:

let result = await rp(params);  // request-promise 
    if (result) {
      let file= new Buffer(result).toString('base64');
    }

Can't save this file back:

let file= new Buffer(stringBase64, 'base64').toString();
      fs.writeFile(fileName, file, 'binary', (error) => {
        if (error) {
          throw error;
        }
      });

For some reason it doesn't work properly. How to save from string to file correctly?
Thank you!
PS pipe is not required.

Answer 1

Found it myself:
You need to insert the binary format.