code: function toFormat (format, options) {
    if (is.object(format) && is.string(format.id)) {
      format = format.id;
    }
    if (format === 'jpg') format = 'jpeg';
    if (!is.inArray(format, ['jpeg', 'png', 'webp', 'tiff', 'raw'])) {
      throw new Error('Unsupported output format ' + format);
    }
    return this[format](options);
  }
docs: Force output to a given format.
  
  @example
  // Convert any input to PNG output
  const data = await sharp(input)
  .toFormat('png')
  .toBuffer();
  
  @param {(String|Object)} format - as a String or an Object with an 'id' attribute
  @param {Object} options - output options
  @returns {Sharp}
  @throws {Error} unsupported format or options