Pipelines

Use |> to pass a value through named filters from left to right. The final value is written with the same context-aware rules as any other expression.

Chain filters

Add one or more stages after an expression.

package views

component Hi(name string) {
	<p>{ name |> trim |> upper }</p>
}

Renders:

<p>ADA</p>

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name |> trim |> upper trims name, then passes that result to upper. Built-in filters include upper, lower, trim, truncate, join, default, printf, urlquery, and dataURL. Custom names come from configured filters.

default preserves the value's type and returns the first non-zero choice:

{count |> default(1)}
{label |> default(shortLabel, "Untitled")}

Pass filter arguments

Put additional arguments in parentheses. The piped value is always the first argument, followed by the values you write.

package views

component Stats(s string, count int) {
	<p>{ s |> trim |> truncate(5) }</p>
	<p>{ count |> printf("%d comments") }</p>
}

Renders:

<p>hello</p><p>42 comments</p>

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Stages with and without arguments can be mixed in the same chain.

Pipe a whole interpolated literal

Put |> after an f literal to filter the complete interpolated string.

package views

component Item(id string) {
	<li>{f`item-@{id}` |> upper}</li>
}

Renders:

<li>ITEM-A&amp;B</li>

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Compare the placement:

{f`item-@{ id |> upper }`} // filters only id
{f`item-@{id}` |> upper}   // filters "item-" and id together

The whole-literal form also works in a braced attribute value: title={f`item-@{id}` |> upper}. Braces are required there; in the direct title=f`item-@{id}` form, pipelines stay inside @{} holes. See Interpolating attribute literals.

Errors

Any pipeline stage may return (T, error). A nil error passes the T value to the next stage; a non-nil error returns from Render immediately, so later stages do not run.

Do not add a try marker: value |> parse? is an error because propagation is automatic. To handle a failure locally, use an explicit Go if statement instead of that stage; see Control flow.

Context-aware output

Pipelines transform values; they do not change the safety rules of the place where the result is written.

package views

component Link(u string) {
	<a href={u |> trim}>x</a>
}

Renders:

<a href="about:invalid#gsx">x</a>

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Here trim runs first, then the URL sink rejects the dangerous scheme. urlquery is useful for encoding one query component, while dataURL builds a base64 data: URL. Neither grants trust: the final URL is still checked for its sink. See Escaping for the URL rules and trusted-value helpers.