.Scratch
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.
{{ .Scratch.Set "greeting" "bonjour" }}
{{ range .Pages }}
{{ .Scratch.Set "greeting" (print "bonjour" .Title) }}
{{ end }}
The local newScratch
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.
{{ $data := newScratch }}
{{ $data.Set "greeting" "hola" }}
Methods
A Scratch has the following methods:
.Set
Set the value of a given key.
{{ $scratch.Set "greeting" "Hello" }}
.Get
Get the value of a given key.
{{ $scratch.Set "greeting" "Hello" }}
----
{{ $scratch.Get "greeting" }} > Hello
.Add
Add a given value to existing value(s) of the given key.
For single values, Add accepts values that support Go’s + operator. If the first Add for a key is an array or slice, the following adds will be appended to that list.
{{ $scratch.Add "greetings" "Hello" }}
{{ $scratch.Add "greetings" "Welcome" }}
----
{{ $scratch.Get "greetings" }} > HelloWelcome
{{ $scratch.Add "total" 3 }}
{{ $scratch.Add "total" 7 }}
----
{{ $scratch.Get "total" }} > 10
{{ $scratch.Add "greetings" (slice "Hello") }}
{{ $scratch.Add "greetings" (slice "Welcome" "Cheers") }}
----
{{ $scratch.Get "greetings" }} > []interface {}{"Hello", "Welcome", "Cheers"}
.SetInMap
Takes a key, mapKey and value and adds a map of mapKey and value to the given key.
{{ $scratch.SetInMap "greetings" "english" "Hello" }}
{{ $scratch.SetInMap "greetings" "french" "Bonjour" }}
----
{{ $scratch.Get "greetings" }} > map[french:Bonjour english:Hello]
.GetSortedMapValues
Return an array of values from key sorted by mapKey.
{{ $scratch.SetInMap "greetings" "english" "Hello" }}
{{ $scratch.SetInMap "greetings" "french" "Bonjour" }}
----
{{ $scratch.GetSortedMapValues "greetings" }} > [Hello Bonjour]
.Delete
Remove the given key.
{{ $scratch.Set "greeting" "Hello" }}
----
{{ $scratch.Delete "greeting" }}
.Values
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.