在golang html / template中格式化float

Question

I want to format float64 value to 2 decimal places in golang html/template say in index.html file. In .go file I can format like:

strconv.FormatFloat(value, 'f', 2, 32)

But I don't know how to format it in template. I am using gin-gonic/gin framework for backend. Any help will be appreciated. Thanks.

Answer 1

You have many options:

• You may decide to format the number e.g. using fmt.Sprintf() before passing it to the template execution (n1)
• Or you may create your own type where you define the String() string method, formatting to your liking. This is checked and used by the template engine (n2).
• You may also call printf directly and explicitly from the template and use custom format string (n3).
• Even though you can call printf directly, this requires to pass the format string. If you don't want to do this every time, you can register a custom function doing just that (n4)

See this example:

type MyFloat float64

func (mf MyFloat) String() string {
    return fmt.Sprintf("%.2f", float64(mf))
}

func main() {
    t := template.Must(template.New("").Funcs(template.FuncMap{
        "MyFormat": func(f float64) string { return fmt.Sprintf("%.2f", f) },
    }).Parse(templ))
    m := map[string]interface{}{
        "n0": 3.1415,
        "n1": fmt.Sprintf("%.2f", 3.1415),
        "n2": MyFloat(3.1415),
        "n3": 3.1415,
        "n4": 3.1415,
    }
    if err := t.Execute(os.Stdout, m); err != nil {
        fmt.Println(err)
    }
}

const templ = `
Number:         n0 = {{.n0}}
Formatted:      n1 = {{.n1}}
Custom type:    n2 = {{.n2}}
Calling printf: n3 = {{printf "%.2f" .n3}}
MyFormat:       n4 = {{MyFormat .n4}}`

Output (try it on the Go Playground):

Number:         n0 = 3.1415
Formatted:      n1 = 3.14
Custom type:    n2 = 3.14
Calling printf: n3 = 3.14
MyFormat:       n4 = 3.14