use localStorage to store form datas

offline-backup.coffee

class OfflineBackup
  constructor: ->
    @pendingRequests = JSON.parse(localStorage.getItem('offline-backups') || '[]')
    $('form.offline-backup').on 'submit', @submitForm
    window.addEventListener 'online', @submitPendingRequests

  submitForm: (e) ->
    unless navigator.onLine

      method = $(this).find('input[name=_method]').val() || $(this).attr('method') || 'get'
      key    = "#{ $(this).attr('action') }:#{ method }:#{ new Date().getTime() }"
      value  = $(this).serialize()

      backupManager.addPendingRequest(key, value)

      e.preventDefault()

  addPendingRequest: (key, value) ->
    localStorage.setItem(key, value)
    backupManager.pendingRequests.push(key)
    localStorage.setItem('offline-backups', JSON.stringify(backupManager.pendingRequests))

  submitPendingRequests: ->
    if request = backupManager.pendingRequests[0]
      data = localStorage.getItem(request)
      [ action, method ] = request.split(':')

      $.ajax
        type: method
        url:  action
        data: data
        success: =>
          backupManager.pendingRequests.shift()
          localStorage.setItem('offline-backups', JSON.stringify(backupManager.pendingRequests))
          localStorage.removeItem(request)
          backupManager.submitPendingRequests()

$ -> window.backupManager = new OfflineBackup

Okay, I went ahead and made this into a plugin: https://github.com/rubysolo/jquery-safetynet

I love it. Definitely going to be using this.