gohugoio-hugo/docs/content/extras/scratch.md

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Scratch -- a "scratchpad" for your node- or page-scoped variables. In most cases you can do well without Scratch, but there are some use cases that aren't solvable with Go's templates without Scratch's help, due to scoping issues.

Scratch is added to both Node and Page -- with following methods:

• Set and Add takes a key and the value to add.
• Get returns the value for the key given.
• SetInMap takes a key, mapKey and value
• GetSortedMapValues returns array of values from key sorted by mapKey

Set and SetInMap can store values of any type. Add accepts values that support Go's + operator.

The scope of the backing data is global for the given Node or Page, and spans partial and shortcode includes.

Sample usage

The usage is best illustrated with some samples:

{{ $.Scratch.Add "a1" 12 }}
{{ $.Scratch.Get "a1" }} {{/* => 12 */}}
{{ $.Scratch.Add "a1" 1 }}
{{ $.Scratch.Get "a1" }} // {{/* => 13 */}}

{{ $.Scratch.Add "a2" "AB" }}
{{ $.Scratch.Get "a2" }} {{/* => AB */}}
{{ $.Scratch.Add "a2" "CD" }}
{{ $.Scratch.Get "a2" }} {{/* => ABCD */}}

{{ $.Scratch.Set "v1" 123 }}
{{ $.Scratch.Get "v1" }}  {{/* => 123 */}}

{{ $.Scratch.SetInMap "a3" "b" "XX" }}
{{ $.Scratch.SetInMap "a3" "a" "AA" }}
{{ $.Scratch.SetInMap "a3" "c" "CC" }}
{{ $.Scratch.SetInMap "a3" "b" "BB" }}
{{ $.Scratch.GetSortedMapValues "a3" }} {{/* => []interface {}{"AA", "BB", "CC"} */}}

Note: The examples above uses the special $ variable, which refers to the top-level node. This is the behavior you most likely want, and will help remove some confusion when using Scratch inside page range loops -- and you start inadvertently calling the wrong Scratch. But there may be use cases for {{ .Scratch.Add "key" "some value" }}.