Brief Tour of Golang `html/template`

README.md

How Do Golang HTML Templates Work?

$ go run main.go
Above
(enabled=NO) Hello World!
Below

document.txt

{{- define "parent" -}}
{{- $child := child .Before .Nested -}}
{{ .Before }}
{{ template "child" $child }}
{{ .After }}
{{ end -}}



{{- define "child" -}}
(enabled={{ if .Disabled }}NO{{ else }}YES{{ end }}) {{ .Message }}
{{- end -}}

main.go

package main

import (
	"fmt"
	"log"
	"os"
	"text/template"
)

type childCtx struct {
	Disabled bool
	Message  string
}

type nestedCtx struct {
	FirstWord  string
	SecondWord string
}

type parentCtx struct {
	Before string
	After  string
	Nested nestedCtx
}

func check(err error) {
	if err != nil {
		log.Fatal(err)
	}
}

func makeChildCtx(before string, nc nestedCtx) (childCtx, error) {
	message := fmt.Sprintf("%s %s!", nc.FirstWord, nc.SecondWord)
	cc := childCtx{
		Disabled: before == "Above",
		Message:  message,
	}
	return cc, nil
}

func main() {
	t, err := template.New("").Funcs(template.FuncMap{"child": makeChildCtx}).ParseFiles("document.txt")
	check(err)

	data := parentCtx{
		Before: "Above",
		After:  "Below",
		Nested: nestedCtx{
			FirstWord:  "Hello",
			SecondWord: "World",
		},
	}
	err = t.ExecuteTemplate(os.Stdout, "parent", data)
	check(err)
}