onSave data gets overridden

[ghost]

In the onSave method below, I add an attribute to the data object called "test" like:

        data.test = 'test'

but after every time the onSave method runs the line below returns undefined.

       console.log(data.test)

How can I add custom values to the data object?

Full code

  storageManager: {
      type: 'remote',
      stepsBeforeSave: 1,
      autosave: true, 
      autoload: true, 
      options: {
        remote: {
          urlLoad: API_URL_GET,
          urlStore: API_URL_INSERT,

          onStore: (data) => {
            data.test = 'test'
            console.log(data.test) // always returns undefined
            console.log('Storing data:', data)
            return { id: PROJECT_ID, data }
          },
          onLoad: (result) => {
            console.log('Loading data:', result)
            const lastItem = result[Object.keys(result).length - 1]
            return lastItem ? JSON.parse(lastItem.data).data : {}
          },
        },
      },
    },
    ```