code: function findAll (state, prefix, filter) {
    var options = {
      include_docs: true
    }
  
    if (prefix) {
      options.startkey = prefix
      options.endkey = prefix + '\uffff'
    }
  
    return state.db.allDocs(options)
  
    .then(function (res) {
      var objects = res.rows
        .filter(isntDesignDoc)
        .map(function (row) {
          return row.doc
        })
  
      return typeof filter === 'function'
        ? objects.filter(filter)
        : objects
    })
  }
docs: finds all existing objects in local database.
  
  @param  {String}   prefix     optional id prefix
  @param  {Function} [filter]   Function returning `true` for any object
  to be returned.
  @return {Promise}