How to use the buffer.Buffer.isEncoding function in buffer

function assertEncoding(encoding) {
  if (encoding && !Buffer.isEncoding(encoding)) {
    throw new Error('Unknown encoding: ' + encoding);
  }
}

function assertEncoding(encoding) {
  if (encoding && !Buffer.isEncoding(encoding)) {
    throw new Error('Unknown encoding: ' + encoding);
  }
}

function assertEncoding(encoding) {
  if (encoding && !Buffer.isEncoding(encoding)) {
    throw new Error('Unknown encoding: ' + encoding);
  }
}

function normalizeEncoding(enc) {
  const nenc = internalUtil.normalizeEncoding(enc);
  if (nenc === undefined) {
    if (Buffer.isEncoding === isEncoding || !Buffer.isEncoding(enc))
      throw new ERR_UNKNOWN_ENCODING(enc);
    return enc;
  }
  return nenc;
}

function assertEncoding(encoding) {
  if (encoding && !Buffer.isEncoding(encoding)) {
    throw new Error('Unknown encoding: ' + encoding);
  }
}

function assertEncoding(encoding) {
  if (encoding && !Buffer.isEncoding(encoding)) {
    throw new Error('Unknown encoding: ' + encoding);
  }
}

function DiffieHellman(sizeOrKey, keyEncoding, generator, genEncoding) {
  if (!(this instanceof DiffieHellman))
    return new DiffieHellman(sizeOrKey, keyEncoding, generator, genEncoding);

  if (typeof sizeOrKey !== 'number' &&
      typeof sizeOrKey !== 'string' &&
      !isArrayBufferView(sizeOrKey)) {
    throw new ERR_INVALID_ARG_TYPE(
      'sizeOrKey',
      ['number', 'string', 'Buffer', 'TypedArray', 'DataView'],
      sizeOrKey
    );
  }

  if (keyEncoding && !Buffer.isEncoding(keyEncoding) &&
      keyEncoding !== 'buffer') {
    genEncoding = generator;
    generator = keyEncoding;
    keyEncoding = false;
  }

  const encoding = getDefaultEncoding();
  keyEncoding = keyEncoding || encoding;
  genEncoding = genEncoding || encoding;

  if (typeof sizeOrKey !== 'number')
    sizeOrKey = toBuf(sizeOrKey, keyEncoding);

  if (!generator)
    generator = DH_GENERATOR;
  else if (typeof generator !== 'number')

options.killSignal = sanitizeKillSignal(options.killSignal);

  var child = spawn(file, args, {
    cwd: options.cwd,
    env: options.env,
    gid: options.gid,
    uid: options.uid,
    shell: options.shell,
    windowsHide: !!options.windowsHide,
    windowsVerbatimArguments: !!options.windowsVerbatimArguments
  });

  var encoding;
  var _stdout;
  var _stderr;
  if (options.encoding !== 'buffer' && Buffer.isEncoding(options.encoding)) {
    encoding = options.encoding;
    _stdout = '';
    _stderr = '';
  } else {
    _stdout = [];
    _stderr = [];
    encoding = null;
  }
  var stdoutLen = 0;
  var stderrLen = 0;
  var killed = false;
  var exited = false;
  var timeoutId;

  var ex = null;

function checkEncoding(encoding: BufferEncoding) {
  if (!Buffer.isEncoding(encoding)) {
    throw new Error(ERRORS.INVALID_ENCODING);
  }
}

function DiffieHellman(sizeOrKey, keyEncoding, generator, genEncoding) {
  if (!(this instanceof DiffieHellman))
    return new DiffieHellman(sizeOrKey, keyEncoding, generator, genEncoding);

  if (typeof sizeOrKey !== 'number' &&
      typeof sizeOrKey !== 'string' &&
      !ArrayBuffer.isView(sizeOrKey)) {
    throw new TypeError('First argument should be number, string, ' +
                        'Buffer, TypedArray, or DataView');
  }

  if (keyEncoding) {
    if (typeof keyEncoding !== 'string' ||
        (!Buffer.isEncoding(keyEncoding) && keyEncoding !== 'buffer')) {
      genEncoding = generator;
      generator = keyEncoding;
      keyEncoding = false;
    }
  }

  keyEncoding = keyEncoding || exports.DEFAULT_ENCODING;
  genEncoding = genEncoding || exports.DEFAULT_ENCODING;

  if (typeof sizeOrKey !== 'number')
    sizeOrKey = toBuf(sizeOrKey, keyEncoding);

  if (!generator)
    generator = DH_GENERATOR;
  else if (typeof generator !== 'number')
    generator = toBuf(generator, genEncoding);