PS C:\Users\jun\Desktop\in_develope\youtube-downloader> node .\app.js
events.js:160
      throw er; // Unhandled 'error' event
      ^

Error: spawn C:\Users\jun\Desktop\in_develope\youtube-downloader\node_modules\youtube-dl\bin\youtube-dl.exe ENOENT
    at exports._errnoException (util.js:1020:11)
    at Process.ChildProcess._handle.onexit (internal/child_process.js:193:32)
    at onErrorNT (internal/child_process.js:367:16)
    at _combinedTickCallback (internal/process/next_tick.js:80:11)
    at process._tickCallback (internal/process/next_tick.js:104:9)
    at Module.runMain (module.js:606:11)
    at run (bootstrap_node.js:389:7)
    at startup (bootstrap_node.js:149:9)
    at bootstrap_node.js:504:3


위와 같은 에러 발생시 이유 : 
mp4.download(url, downloadPath, fileName);
호출시 downloadPath부분 경로가 존재하지 않는 경우 이러한 에러가 발생한다.