docuseal/app/javascript/elements/file_dropzone.js

import { actionable } from '@github/catalyst/lib/actionable'
import { target, targetable } from '@github/catalyst/lib/targetable'

export default actionable(targetable(class extends HTMLElement {
  static [target.static] = [
    'loading',
    'icon',
    'input'
  ]

  connectedCallback () {
    if (this.dataset.isDirectUpload === 'true') {
      import('@rails/activestorage')
    }

    this.addEventListener('drop', this.onDrop)

    this.addEventListener('dragover', (e) => e.preventDefault())

    document.addEventListener('turbo:submit-end', this.toggleLoading)
  }

  disconnectedCallback () {
    document.removeEventListener('turbo:submit-end', this.toggleLoading)
  }

  onDrop (e) {
    e.preventDefault()

    this.input.files = e.dataTransfer.files

    this.uploadFiles(e.dataTransfer.files)
  }

  onSelectFiles (e) {
    e.preventDefault()

    this.uploadFiles(this.input.files)
  }

  toggleLoading = () => {
    this.loading.classList.toggle('hidden')
    this.icon.classList.toggle('hidden')
    this.classList.toggle('opacity-50')
  }

  async uploadFiles (files) {
    this.toggleLoading()

    if (this.dataset.isDirectUpload === 'true') {
      const { DirectUpload } = await import('@rails/activestorage')

      await Promise.all(
        Array.from(files).map(async (file) => {
          const upload = new DirectUpload(
            file,
            '/direct_uploads',
            this.input
          )

          return new Promise((resolve, reject) => {
            upload.create((error, blob) => {
              if (error) {
                console.error(error)

                return reject(error)
              } else {
                return resolve(blob)
              }
            })
          }).catch((error) => {
            console.error(error)
          })
        })
      ).then((blobs) => {
        if (this.dataset.submitOnUpload) {
          this.querySelectorAll('[name="blob_signed_ids[]"]').forEach((e) => e.remove())
        }

        blobs.forEach((blob) => {
          const input = document.createElement('input')

          input.type = 'hidden'
          input.name = 'blob_signed_ids[]'
          input.value = blob.signed_id

          this.append(input)
        })

        if (this.dataset.submitOnUpload) {
          this.closest('form').querySelector('button[type="submit"]').click()
        }
      }).finally(() => {
        this.toggleLoading()
      })
    } else {
      if (this.dataset.submitOnUpload) {
        this.closest('form').querySelector('button[type="submit"]').click()
      }
    }
  }
}))