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

write(filepath, contents, options) {
    if (!options) {
      options = {}
    }
    // Create path, if necessary.
    this.mkdir(path.dirname(filepath))
    try {
      // If contents is already a Buffer, don't try to encode it. If no encoding was specified, use the default.
      if (!Buffer.isBuffer(contents)) {
        contents = iconv.encode(contents, options.encoding || this.config.encoding)
      }
      // Actually write this.
      fs.writeFileSync(filepath, contents)

      return true
    }
    catch (e) {
      this.notifyError(`Unable to write ${filepath} file (Error code: ${e.code}).`, e)
    }
  }

function writeOrBuffer(stream, state, chunk, encoding, cb) {
  chunk = decodeChunk(state, chunk, encoding);

  if (Buffer.isBuffer(chunk))
    encoding = 'buffer';
  var len = state.objectMode ? 1 : chunk.length;

  state.length += len;

  var ret = state.length < state.highWaterMark;
  // we must ensure that previous needDrain will not be reset to false.
  if (!ret)
    state.needDrain = true;

  if (state.writing || state.corked) {
    var last = state.lastBufferedRequest;
    state.lastBufferedRequest = new WriteReq(chunk, encoding, cb);
    if (last) {
      last.next = state.lastBufferedRequest;
    } else {

Binary.prototype.value = function value(asRaw) {
  asRaw = asRaw == null ? false : asRaw;  

  // Optimize to serialize for the situation where the data == size of buffer
  if(asRaw && typeof Buffer != 'undefined' && Buffer.isBuffer(this.buffer) && this.buffer.length == this.position)
    return this.buffer;
  
  // If it's a node.js buffer object
  if(typeof Buffer != 'undefined' && Buffer.isBuffer(this.buffer)) {
    return asRaw ? this.buffer.slice(0, this.position) : this.buffer.toString('binary', 0, this.position);
  } else {
    if(asRaw) {
      // we support the slice command use it
      if(this.buffer['slice'] != null) {
        return this.buffer.slice(0, this.position);
      } else {
        // Create a new buffer to copy content to
        var newBuffer = Object.prototype.toString.call(this.buffer) == '[object Uint8Array]' ? new Uint8Array(new ArrayBuffer(this.position)) : new Array(this.position);
        // Copy content
        for(var i = 0; i < this.position; i++) {
          newBuffer[i] = this.buffer[i];
        }
        // Return the buffer
        return newBuffer;
      }

buffer = new Buffer(this.buffer.length + string.length);
      this.buffer.copy(buffer, 0, 0, this.buffer.length);      
    } else if(Object.prototype.toString.call(this.buffer) == '[object Uint8Array]') {
      // Create a new buffer
      buffer = new Uint8Array(new ArrayBuffer(this.buffer.length + string.length))
      // Copy the content
      for(var i = 0; i < this.position; i++) {
        buffer[i] = this.buffer[i];
      }
    }
    
    // Assign the new buffer
    this.buffer = buffer;
  }

  if(typeof Buffer != 'undefined' && Buffer.isBuffer(string) && Buffer.isBuffer(this.buffer)) {
    string.copy(this.buffer, offset, 0, string.length);
    this.position = (offset + string.length) > this.position ? (offset + string.length) : this.position;
    // offset = string.length
  } else if(typeof Buffer != 'undefined' && typeof string == 'string' && Buffer.isBuffer(this.buffer)) {
    this.buffer.write(string, offset, 'binary');
    this.position = (offset + string.length) > this.position ? (offset + string.length) : this.position;
    // offset = string.length;
  } else if(Object.prototype.toString.call(string) == '[object Uint8Array]' 
    || Object.prototype.toString.call(string) == '[object Array]' && typeof string != 'string') {      
    for(var i = 0; i < string.length; i++) {
      this.buffer[offset++] = string[i];
    }    

    this.position = offset > this.position ? offset : this.position;
  } else if(typeof string == 'string') {
    for(var i = 0; i < string.length; i++) {

function () {
      var body = Buffer.isBuffer(arr[0]) ? Buffer.concat(arr)
        : arr.join('')
      this.emit('data', body)
      this.emit('end')
      if(callback) callback(null, body)
    })
}

function validChunk(stream, state, chunk, cb) {
  var valid = true;

  if (!(Buffer.isBuffer(chunk)) &&
      typeof chunk !== 'string' &&
      chunk !== null &&
      chunk !== undefined &&
      !state.objectMode) {
    var er = new TypeError('Invalid non-string/buffer chunk');
    stream.emit('error', er);
    process.nextTick(cb, er);
    valid = false;
  }
  return valid;
}

function chunkInvalid(state, chunk) {
  var er = null;
  if (!Buffer.isBuffer(chunk) &&
      'string' !== typeof chunk &&
      chunk !== null &&
      chunk !== undefined &&
      !state.objectMode &&
      !er) {
    er = new TypeError('Invalid non-string/buffer chunk');
  }
  return er;
}

function chunkInvalid(state, chunk) {
  var er = null;
  if (!Buffer.isBuffer(chunk) && typeof chunk !== 'string' && chunk !== null && chunk !== undefined && !state.objectMode) {
    er = new TypeError('Invalid non-string/buffer chunk');
  }
  return er;
}

var is_pem = function (indata) {
    if (indata.constructor === Uint8Array || Buffer.isBuffer(indata)) {
        if ((indata[0] === 0x2D) &&
                (indata[1] === 0x2D) &&
                (indata[2] === 0x2D) &&
                (indata[3] === 0x2D) &&
                (indata[4] === 0x2D)) {
            return true;
        }
    }
    if ((typeof indata) === 'string') {
        return indata.indexOf('-----') === 0;
    }
};

function chunkInvalid(state, chunk) {
  var er = null;
  if (!Buffer.isBuffer(chunk) &&
      'string' !== typeof chunk &&
      chunk !== null &&
      chunk !== undefined &&
      !state.objectMode) {
    er = new TypeError('Invalid non-string/buffer chunk');
  }
  return er;
}