asciinema.org/app/models/frame_diff.rb

class FrameDiff

  def initialize(line_changes, cursor_changes)
    @line_changes = line_changes
    @cursor_changes = cursor_changes
  end

  def as_json(*)
    json = {}
    json[:lines] = line_changes unless line_changes.blank?
    json[:cursor] = cursor_changes unless cursor_changes.blank?

    json
  end

  private

  attr_reader :line_changes, :cursor_changes

end