How to use the base64-js.fromByteArray function in base64-js

checkAtHash(accessToken, idClaims) {
        if (!accessToken || !idClaims || !idClaims.at_hash ) return true;
        var tokenHash: Array = sha256(accessToken, { asBytes: true });
        var leftMostHalf = tokenHash.slice(0, (tokenHash.length/2) );
        var tokenHashBase64 = fromByteArray(leftMostHalf);
        var atHash = tokenHashBase64.replace(/\+/g, "-").replace(/\//g, "_").replace(/=/g, "");
        var claimsAtHash = idClaims.at_hash.replace(/=/g, "");
        
        var atHash = tokenHashBase64.replace(/\+/g, "-").replace(/\//g, "_").replace(/=/g, "");

        if (atHash != claimsAtHash) {
            console.warn("exptected at_hash: " + atHash);    
            console.warn("actual at_hash: " + claimsAtHash);
        }
        
        
        return (atHash == claimsAtHash);
    }

function base64Slice (buf, start, end) {
  if (start === 0 && end === buf.length) {
    return base64.fromByteArray(buf)
  } else {
    return base64.fromByteArray(buf.slice(start, end))
  }
}

function _base64Slice (buf, start, end) {
  if (start === 0 && end === buf.length) {
    return base64.fromByteArray(buf)
  } else {
    return base64.fromByteArray(buf.slice(start, end))
  }
}

function base64Slice (buf, start, end) {
  if (start === 0 && end === buf.length) {
    return base64.fromByteArray(buf)
  } else {
    return base64.fromByteArray(buf.slice(start, end))
  }
}

function base64Slice (buf, start, end) {
  if (start === 0 && end === buf.length) {
    return base64.fromByteArray(buf)
  } else {
    return base64.fromByteArray(buf.slice(start, end))
  }
}

function base64Slice (buf, start, end) {
  if (start === 0 && end === buf.length) {
    return base64.fromByteArray(buf)
  } else {
    return base64.fromByteArray(buf.slice(start, end))
  }
}

}).then(cred => {
        let ctHeaders = new Headers()
        ctHeaders.append('Content-Type', 'application/json')
        fetch(`/auth/${encodeURIComponent(username)}/newSession/`, {method: 'POST', headers: ctHeaders, body: JSON.stringify({
          type: 'fido2',
          clientDataJSON: String.fromCharCode.apply(null, new Uint8Array(cred.response.clientDataJSON)),
          authenticatorData: base64js.fromByteArray(new Uint8Array(cred.response.authenticatorData)),
          signature: base64js.fromByteArray(new Uint8Array(cred.response.signature)),
          userHandle: base64js.fromByteArray(new Uint8Array(cred.response.userHandle))
        })}).then(FetchErrorPromise.then, FetchErrorPromise.error).then(res => res.json()).then(json => {
          let token = json.authToken
          AppState.dispatch({type: 'finish-login', token})
        }, err => {
          this.setState({
            requestState: null, lastError: err
          })
        })
      }, err => {
        this.setState({requestState: null, lastError: err})

_testSecretBox1() {

    const k = Base64.fromByteArray(new Uint8Array([
      0x1b, 0x27, 0x55, 0x64, 0x73, 0xe9, 0x85, 0xd4, 0x62, 0xcd, 0x51, 0x19, 0x7a, 0x9a, 0x46, 0xc7,
      0x60, 0x09, 0x54, 0x9e, 0xac, 0x64, 0x74, 0xf2, 0x06, 0xc4, 0xee, 0x08, 0x44, 0xf6, 0x83, 0x89]))

    const n = Base64.fromByteArray(new Uint8Array([
      0x69, 0x69, 0x6e, 0xe9, 0x55, 0xb6, 0x2b, 0x73, 0xcd, 0x62, 0xbd, 0xa8,
      0x75, 0xfc, 0x73, 0xd6, 0x82, 0x19, 0xe0, 0x03, 0x6b, 0x7a, 0x0b, 0x37]))

    const m = Base64.fromByteArray(new Uint8Array([
      0xbe, 0x07, 0x5f, 0xc5, 0x3c, 0x81, 0xf2, 0xd5, 0xcf, 0x14, 0x13, 0x16,
      0xeb, 0xeb, 0x0c, 0x7b, 0x52, 0x28, 0xc5, 0x2a, 0x4c, 0x62, 0xcb, 0xd4,
      0x4b, 0x66, 0x84, 0x9b, 0x64, 0x24, 0x4f, 0xfc, 0xe5, 0xec, 0xba, 0xaf,
      0x33, 0xbd, 0x75, 0x1a, 0x1a, 0xc7, 0x28, 0xd4, 0x5e, 0x6c, 0x61, 0x29,
      0x6c, 0xdc, 0x3c, 0x01, 0x23, 0x35, 0x61, 0xf4, 0x1d, 0xb6, 0x6c, 0xce,
      0x31, 0x4a, 0xdb, 0x31, 0x0e, 0x3b, 0xe8, 0x25, 0x0c, 0x46, 0xf0, 0x6d,
      0xce, 0xea, 0x3a, 0x7f, 0xa1, 0x34, 0x80, 0x57, 0xe2, 0xf6, 0x55, 0x6a,
      0xd6, 0xb1, 0x31, 0x8a, 0x02, 0x4a, 0x83, 0x8f, 0x21, 0xaf, 0x1f, 0xde,

function base64Slice (buf, start, end) {
  if (start === 0 && end === buf.length) {
    return base64.fromByteArray(buf)
  } else {
    return base64.fromByteArray(buf.slice(start, end))
  }
}

function base64Slice (buf, start, end) {
  if (start === 0 && end === buf.length) {
    return base64.fromByteArray(buf)
  } else {
    return base64.fromByteArray(buf.slice(start, end))
  }
}