old_contents: const cheerio = require('cheerio');
  const request = require('request');
  const fs = require('fs');
  const _ = require('lodash');
  
  module.exports = save;
  
  /**
   * @param  {string} identifier media ID or URL
   * @return {Promise}
   */
  function save(identifier, dir) {
    return new Promise((resolve, reject) => {
      const url = identifier.substring(0, 8) === 'https://' ? identifier : `https://www.instagram.com/p/${identifier}/`;
  
      request(url, (err, response, body) => {
        if (err) {
          return reject({
            message: `Failed to request resource`,
            url,
            error: err
          });
        }
  
        const $ = cheerio.load(body);
        const canonicalUrl = $('link[rel="canonical"]').attr('href');
  
        if (!canonicalUrl) {
          return reject({
            message: `Invalid media ID`,
            url
          });
        }
  
        const isVideo = $('meta[name="medium"]').attr('content') === 'video';
        const mimeType = isVideo ? $('meta[property="og:video:type"]').attr('content') : 'image/jpeg';
        const mediaId = canonicalUrl.split('/')[4];
        const filename = createFilename(mediaId, mimeType, dir);
        const downloadUrl = isVideo ? $('meta[property="og:video"]').attr('content') : $('meta[property="og:image"]').attr('content');
  
        request.head(downloadUrl, error => {
          if (error) {
            return reject({
              message: `Download failed`,
              url,
              error
            });
          }
  
          request(downloadUrl)
            .pipe(fs.createWriteStream(filename))
            .on('close', () => {
              return resolve({
                file: filename,
                type: isVideo ? 'video' : 'photo',
                mimeType,
                url,
                source: downloadUrl
              });
            });
        });
      });
    });
  }
  
  /**
   * @param  {string} mediaId
   * @param  {string} mimeType
   * @param  {string} dir
   * @return {string}
   */
  function createFilename(mediaId, mimeType, dir) {
    const mimeTypeToExtensionMap = {
      'video/mp4': '.mp4',
      'video/ogg': '.ogg',
      'video/webm': '.webm',
      'image/jpeg': '.jpg'
    };
  
    const extension = _.get(mimeTypeToExtensionMap, mimeType, '.jpg');
  
    return `${dir}/${mediaId}${extension}`;
  }
  
new_contents: const cheerio = require('cheerio');
  const request = require('request');
  const fs = require('fs');
  const _ = require('lodash');
  
  module.exports = save;
  
  /**
   * @param  {string} identifier media ID or URL
   * @return {Promise}
   */
  function save(identifier, dir) {
    return new Promise((resolve, reject) => {
      const url = identifier.substring(0, 8) === 'https://' ? identifier : `https://www.instagram.com/p/${identifier}/`;
  
      request(url, (err, response, body) => {
        if (err) {
          return reject({
            message: `Failed to request resource`,
            url,
            error: err
          });
        }
  
        const $ = cheerio.load(body);
        const canonicalUrl = $('link[rel="canonical"]').attr('href');
  
        if (!canonicalUrl) {
          return reject({
            message: `Invalid media ID`,
            url
          });
        }
  
        const isVideo = $('meta[name="medium"]').attr('content') === 'video';
        const mimeType = isVideo ? $('meta[property="og:video:type"]').attr('content') : 'image/jpeg';
        const mediaId = canonicalUrl.split('/')[4];
        const filename = createFilename(mediaId, mimeType, dir);
        const downloadUrl = isVideo ? $('meta[property="og:video"]').attr('content') : $('meta[property="og:image"]').attr('content');
  
        request.head(downloadUrl, error => {
          if (error) {
            return reject({
              message: `Download failed`,
              url,
              error
            });
          }
  
          request(downloadUrl)
            .pipe(fs.createWriteStream(filename))
            .on('close', () => {
              return resolve({
                file: filename,
                type: isVideo ? 'video' : 'photo',
                mimeType,
                url,
                source: downloadUrl
              });
            });
        });
      });
    });
  }
  
  /**
   * @param  {string} mediaId
   * @param  {string} mimeType
   * @param  {string} dir
   * @return {string}
   */
  function createFilename(mediaId, mimeType, dir) {
    const mimeTypeToExtensionMap = {
      'video/mp4': '.mp4',
      'video/ogg': '.ogg',
      'video/webm': '.webm',
      'image/jpeg': '.jpg'
    };
  
    const extension = _.get(mimeTypeToExtensionMap, mimeType);
  
    return `${dir}/${mediaId}${extension}`;
  }
  
subject: Remove redundant default extension