How Do I Call Custom Methods from Go HTML Templates?

Calling Methods from Go Templates

In Go, you can define custom methods for data types. How do you call these methods from an HTML template in Go?

Consider the following example:

type Person struct {
  Name string
}
func (p *Person) Label() string {
  return "This is " + p.Name
}

To call the Label method from a template, use the following syntax:

{{ .Label }}

Note that you omit the parentheses when calling the method.

Here's a complete Go program that demonstrates the usage of method calls in templates:

package main

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

type Person string

func (p Person) Label() string {
    return "This is " + string(p)
}

func main() {
    tmpl, err := template.New("").Parse(`{{.Label}}`)
    if err != nil {
        log.Fatalf("Parse: %v", err)
    }
    tmpl.Execute(os.Stdout, Person("Bob"))
}

When you run this program, it will output:

This is Bob

According to the Go template documentation, you can call any method that returns one value (of any type) or two values if the second one is of type error. If the second returned value is an error, the Execute function will return that error as non-nil and discontinue the template execution.

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