Scratch is a Hugo feature designed to conveniently manipulate data in a Go Template world. It is either a Page or Shortcode method for which the resulting data will be attached to the given context, or it can live as a unique instance stored in a variable.
Contexted .Scratch vs. local newScratch
Since Hugo 0.43, there are two different ways of using Scratch:
The Page’s .Scratch
.Scratch is available as a Page method or a Shortcode method and attaches the “scratched” data to the given page. Either a Page or a Shortcode context is required to use .Scratch.
A Scratch instance can also be assigned to any variable using the newScratch function. In this case, no Page or Shortcode context is required and the scope of the scratch is only local. The methods detailed below are available from the variable the Scratch instance was assigned to.
Return the raw backing map. Note that you should only use this method on the locally scoped Scratch instances you obtain via newScratch, not .Page.Scratch etc., as that will lead to concurrency issues.