hugo/docs/content/en/functions/default.md

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default	Allows setting a default value that can be returned if a first value is not set.	Returns a default value if a value is not set when checked.	defaults	functions	docs parent functions		default DEFAULT INPUT

default checks whether a given value is set and returns a default value if it is not. Set in this context means different things depending on the data type:

• non-zero for numeric types and times
• non-zero length for strings, arrays, slices, and maps
• any boolean or struct value
• non-nil for any other types

default function examples reference the following content page:

{{< code file="content/posts/default-function-example.md" >}}

title: Sane Defaults seo_title: date: 2017-02-18 font: oldparam: The default function helps make your templating DRYer. newparam:

{{< /code >}}

default can be written in more than one way:

{{ .Params.font | default "Roboto" }}
{{ default "Roboto" .Params.font }}

Both of the above default function calls return Roboto.

A default value, however, does not need to be hard coded like the previous example. The default value can be a variable or pulled directly from the front matter using dot notation:

{{ $old := .Params.oldparam }}
<p>{{ .Params.newparam | default $old }}</p>

Which would return:

<p>The default function helps make your templating DRYer.</p>

And then using dot notation

<title>{{ .Params.seo_title | default .Title }}</title>

Which would return

<title>Sane Defaults</title>

The following have equivalent return values but are far less terse. This demonstrates the utility of default:

Using if:

<title>{{ if .Params.seo_title }}{{ .Params.seo_title }}{{ else }}{{ .Title }}{{ end }}</title>
=> Sane Defaults

Using with:

<title>{{ with .Params.seo_title }}{{ . }}{{ else }}{{ .Title }}{{ end }}</title>
=> Sane Defaults