How to put base64 stream in a variable

I have right now the result of the basae64 encoding in the stdout
(response.pipe(new Base64Encode()).pipe(process.stdout);)

I'm looking how to put this result in the variable "base64"

const request = require('request');
const unirest = require('unirest');
var {
    Base64Encode
} = require('base64-stream');


process.env['NODE_TLS_REJECT_UNAUTHORIZED'] = 0;


var theimg = request.get('https://127.0.0.1/cgi-bin/snapshot.cgi?channel=1', {
        'auth': {
            'user': 'Username',
            'pass': 'Password',
            'sendImmediately': false
        }
    },
    function (error, response, body) {
        if (error) {
            return console.error('failed:', error);
        }
    }).on('response', function (response) {
    //console.log(response.statusCode) // 200
    //console.log(response.headers['content-type']) // 'image/png'


    var base64;


    if (response.statusCode == 200) {
        response.pipe(new Base64Encode()).pipe(process.stdout);
    }


    /*unirest.post("https://example.com/api/1/upload/?key=123456789abcd")
        .header('Accept', 'application/json')
        .send({
            source: base64,
            format: 'txt'
        })
        .end(function (response) {
            console.log("IMG:" + response.body);
        })*/
});

Select allOpen in new window