Browser console support for shellking4, see https://gist.github.com/loilo/ed43739361ec718129a15ae5d531095b?permalink_comment_id=3649980#gistcomment-3649980

export.js

// Copy this whole snippet to your browser console

var dbName = prompt("What's the name of the database to export?")

;(async () => {
try {
  var dbExists = await new Promise(resolve => {
    var request = window.indexedDB.open(dbName)
    request.onupgradeneeded = e => {
      e.target.transaction.abort()
      resolve(false)
    }
    request.onerror = () => resolve(true)
    request.onsuccess = () => resolve(true)
  })

  if (!dbExists) {
    throw new Error('Database does not exist')
  }

  var idbDatabase = await new Promise((resolve, reject) => {
    var request = window.indexedDB.open(dbName)
    request.onerror = () => reject('Could not open the database')
    request.onsuccess = () => resolve(request.result)
  })

  var json = await new Promise((resolve, reject) => {
    const exportObject = {}
    if (idbDatabase.objectStoreNames.length === 0) {
      resolve(JSON.stringify(exportObject))
    } else {
      const transaction = idbDatabase.transaction(
        idbDatabase.objectStoreNames,
        'readonly'
      )
  
      transaction.addEventListener('error', reject)
  
      for (const storeName of idbDatabase.objectStoreNames) {
        const allObjects = []
        transaction
          .objectStore(storeName)
          .openCursor()
          .addEventListener('success', event => {
            const cursor = event.target.result
            if (cursor) {
              // Cursor holds value, put it into store data
              allObjects.push(cursor.value)
              cursor.continue()
            } else {
              // No more values, store is done
              exportObject[storeName] = allObjects
  
              // Last store was handled
              if (
                idbDatabase.objectStoreNames.length ===
                Object.keys(exportObject).length
              ) {
                resolve(JSON.stringify(exportObject))
              }
            }
          })
      }
    }
  })

  console.log(' ')
  console.log('Database has been exported:')
  console.log(' ')
  console.log(json)
  console.log(' ')
} catch(error) {
  console.error(error)
}
})()