Golang : How to call function inside template with template.FuncMap

Alright, just a simple tutorial on how to call your own function inside HTML template. For this example, we will "import" the WordWrap function into the template using the template.FuncMap() and call it from inside a template.

Here you go!

 package main

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

 const TextData = `After wordwrap : 
  {{(wordwrap .Message 3) }}` // change 3 to 2 or 1 and see how it goes

 var templateDataMap = map[string]interface{}{}

 func main() {

  templateDataMap["Message"] = "this is a simple message string"

  var ownFuncs = template.FuncMap{"wordwrap": WordWrap}

  var PageBody = template.Must(template.New("PageBody").Funcs(ownFuncs).Parse(TextData))

  if err := PageBody.ExecuteTemplate(os.Stdout, "PageBody", templateDataMap); err != nil { // replace os.Stdout with w http.ResponseWriter for html/template

 fmt.Println(err)
  }

 }

 func WordWrap(s string, limit int) string {

  if strings.TrimSpace(s) == "" {
 return s
  }

  // convert string to slice
  strSlice := strings.Fields(s)

  var result string = ""

  for len(strSlice) >= 1 {
 // convert slice/array back to string
 // but insert \r\n at specified limit

 result = result + strings.Join(strSlice[:limit], " ") + "\r\n"
 //result = result + strings.Join(strSlice[:limit], " ") + "<br>"  this is for HTML

 // discard the elements that were copied over to result
 strSlice = strSlice[limit:]

 // change the limit
 // to cater for the last few words in
 //
 if len(strSlice) < limit {
 limit = len(strSlice)
 }

  }

  return result

 }

Sample output:

this is

a simple

message string

References:

https://www.socketloop.com/references/golang-html-template-funcmap-type-examples

https://www.socketloop.com/tutorials/golang-populate-dropdown-with-html-template-example