In html/template, is it possible to "extend" a block?

Getting Help
1

Hello everyone, I think it’s better to explain my question via code:

{{define "base"}}
    <h1>An example template</h1>
    {{block "sidebar" .}}
        <p>My default sidebar content</p>
    {{end}}
{{end}}

<!-- child1.html -->
{{template "base" .}}

<!-- 
    I want this page's sidebar to show:
    <p>My default sidebar content</p>
-->
<!-- 
    Answer: just do nothing
-->

<!-- child2.html -->

{{template "base" .}}
<!-- 
    I want this page to show:
    <p>My default sidebar content</p>
    <p>My custom sidebar content</p>
-->

{{define "sidebar"}}
    <!-- Answer: ??? -->
{{end}}

<!-- child3.html -->

{{template "base" .}}
<!-- 
    I want this page's sidebar to show:
    <p>My custom sidebar content</p>
    <p>My default sidebar content</p>
-->

{{define "sidebar"}}
    <!-- Answer: ??? -->
{{end}}

I’ve used this particular feature from Django[1] and Laravel[2], and am wondering how to implement it with Go templates.

Thank you!

[1] How to override templates | Django documentation | Django
[2] Blade Templates - Laravel - The PHP Framework For Web Artisans

2

This might be of use:

3

I was reading this thread earlier as well – it did help me understand how to correctly order my template parsing so overriding works properly. Unfortunately I don’t think it covers my particular question.

4

As I understand it you want a base template and use templates for each page inside the base template. I tried to achieve this, but I gave up. Now I am using “components” at page level. Not bad approach, but not the way I wanted from the beginning. I have found this good enough and easy to reuse components instead.

5

I’m not sure I fully understand what you’re after, but what about something like this?

package main

import (
	"fmt"
	"html/template"
	"os"
)

var baseTemplate = `{{define "base"}}
    <h1>An example template</h1>
        <p>My default sidebar content</p>
        {{block "sidebar" .}}
        {{end}}
{{end}}`

var childTemplate = `{{template "base" .}}`

var childTemplateWithCustom = `{{template "base" .}}
{{define "sidebar"}}<p>Custom sidebar template</p>{{end}}`

func main() {
	baseTmpl := template.Must(template.New("baseTemplate").Parse(baseTemplate))

	childTmpl, _ := template.Must(baseTmpl.Clone()).Parse(childTemplate)
	fmt.Println("No custom content:")
	childTmpl.Execute(os.Stdout, nil)

	childTmplWithCustom, _ := template.Must(baseTmpl.Clone()).Parse(childTemplateWithCustom)
	fmt.Println("Custom content:")
	childTmplWithCustom.Execute(os.Stdout, nil)
}

… which outputs:

No custom content:

    <h1>An example template</h1>
        <p>My default sidebar content</p>
        
        
Custom content:

    <h1>An example template</h1>
        <p>My default sidebar content</p>
        <p>Custom sidebar template</p>

You can run it on the go playground if you want. Also check out the docs for sharing template building blocks with other templates:

They call them “driver templates” but the idea is basically re-usable base templates that you .Clone for use in other templates.

6

Thanks for this, but this doesn’t allow me to replace the default sidebar at all because it’s outside of the block. I think I got enough feedback from other sources as well that there’s no exact way to do this with html/template. I just resorted to this implementation that is close enough to what I want:

I appreciate the help, really!

7

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