title: How can make folder with Firebase Cloud Functions Storage
body: <p><strong>how can I make folder "posts" ?</strong></p>
  
  <blockquote>
    <p>bucket --> gs://app.appspot.com/posts</p>
  </blockquote>
  
  <p><strong>code</strong></p>
  
  <pre><code>exports.generateThumbnail = functions.storage.object()
    .onChange(event =&gt; {
      const object = event.data
      const filePath = object.name
      const fileName = filePath.split('/').pop()
      const fileBucket = object.bucket;
      const bucket = gcs.bucket(fileBucket)
      const tempFilePath = `/posts/${fileName}`
  
      return bucket.file(filePath).download({
        destination: tempFilePath
      })
      .then(() =&gt; {
        console.log('image downloaded locally to', tempFilePath)
        return spawn('convert', [tempFilePath, '-thumbnail', '400x400&gt;', tempFilePath])
      })
      .then(() =&gt; {
        console.log('thumbnail created')
        // match end of string that contains a slash followed by 0 or more characters that are not a slash:
        const thumbFilePath = filePath.replace(/(\/)?([^\/]*)*/, '$1thumb_$2')
            console.log('afoter=thumbFilePath=='+thumbFilePath);
        return bucket.upload(tempFilePath, {
          destination: thumbFilePath
        })
      })
  
    });
  </code></pre>
  
  <p><strong>error</strong> </p>
  
  <blockquote>
    <p>Error: EROFS: read-only file system, open  '/posts/image.jpg'?</p>
  </blockquote>