Body object contents in "Elasticsearch Node.js Client" API return values

The documentation forElasticsearch Node.js Client says that "The returned value of every API call is formed as follows":

{
  body: object | boolean
  statusCode: number
  headers: object
  warnings: [string],
  meta: object
}

My question is how to interpret the "body: object"; i.e., how to know what fields the body actually contains and how to look at them.

I cannot find anything in the documentation on this.