code: function type(buffer) {
      if (buffer[0] === 0x89 && buffer[1] === 0x50 && buffer[2] === 0x4E &&
          buffer[3] === 0x47 && buffer[4] === 0x0D && buffer[5] === 0x0A &&
          buffer[6] === 0x1A && buffer[7] === 0x0A) {
          return 'png';
      } else if (buffer[0] === 0xFF && buffer[1] === 0xD8 &&
          buffer[buffer.length - 2] === 0xFF && buffer[buffer.length - 1] === 0xD9) {
          return 'jpg';
      } else if (buffer[0] === 0x47 && buffer[1] === 0x49 && buffer[2] === 0x46 &&
          buffer[3] === 0x38 && (buffer[4] === 0x39 || buffer[4] === 0x37) &&
          buffer[5] === 0x61) {
          return 'gif';
      } else if (buffer[0] === 0x52 && buffer[1] === 0x49 && buffer[2] === 0x46 && buffer[3] === 0x46 &&
          buffer[8] === 0x57 && buffer[9] === 0x45 && buffer[10] === 0x42 && buffer[11] === 0x50) {
          return 'webp';
      // deflate: recklessly assumes contents are PBF.
      } else if (buffer[0] === 0x78 && buffer[1] === 0x9C) {
          return 'pbf';
      // gzip: recklessly assumes contents are PBF.
      } else if (buffer[0] === 0x1F && buffer[1] === 0x8B) {
          return 'pbf';
      }
      return false;
  }
docs: Given a buffer of unknown data, return either a format as an extension
  string or false if the type cannot be determined.
  
  Potential options are:
  
  * png
  * pbf
  * jpg
  * webp
  
  @param {Buffer} buffer input
  @returns {String|boolean} identifier