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Statements

Control flow​

Within a templ element, a subset of Go statements can be used directly.

These Go statements can be used to conditionally render child elements, or to iterate variables.

For individual implementation guides see:

if/switch/for within text​

Go statements can be used without any escaping to make it simple for developers to include them.

The templ parser assumes that text that starts with if, switch or for denotes the start of one of those expressions as per this example.

show-hello.templ
package main

templ showHelloIfTrue(b bool) {
	<div>
		if b {
			<p>Hello</p>
		}
	</div>
}

If you need to start a text block with the words if, switch, or for:

  • Use a Go string expression.
  • Capitalise if, switch, or for.
paragraph.templ
package main

templ display(price float64, count int) {
	<p>Switch to Linux</p>
	<p>{ `switch to Linux` }</p>
	<p>{ "for a day" }</p>
	<p>{ fmt.Sprintf("%f", price) }{ "for" }{ fmt.Sprintf("%d", count) }</p>
	<p>{ fmt.Sprintf("%f for %d", price, count) }</p>
}

Design considerations​

We decided to not require a special prefix for if, switch and for expressions on the basis that we were more likely to want to use a Go control statement than start a text run with those strings.

To reduce the risk of a broken control statement, resulting in printing out the source code of the application, templ will complain if a text run starts with if, switch or for, but no opening brace { is found.

For example, the following code causes the templ parser to return an error:

broken-if.templ
package main

templ showIfTrue(b bool) {
	if b 
	  <p>Hello</p>
	}
}
note

Note the missing { on line 4.

The following code also produces an error, since the text run starts with if, but no opening { is found.

paragraph.templ
package main

templ text(b bool) {
	<p>if a tree fell in the woods</p>
}
note

This also applies to for and switch statements.

To resolve the issue:

  • Use a Go string expression.
  • Capitalise if, switch, or for.
paragraph.templ
package main

templ display(price float64, count int) {
	<p>Switch to Linux</p>
	<p>{ `switch to Linux` }</p>
	<p>{ "for a day" }</p>
	<p>{ fmt.Sprintf("%f", price) }{ "for" }{ fmt.Sprintf("%d", count) }</p>
	<p>{ fmt.Sprintf("%f for %d", price, count) }</p>
}