How Do You Format Floating-Point Numbers in Go HTML/Templates?

Formatting Floats in Go HTML/Template

When working with floating-point numbers in Go templates, it is often necessary to format them for display purposes. Here are various methods for formatting floats in html/template:

1. Pre-formatting in Controller

Before passing the float to the template, you can format it in the controller using strconv.FormatFloat().

2. Custom Types

Create a custom type that implements the String() method, which formats the float to the desired precision. The template engine will automatically use this method for formatting.

3. Explicit printf in Template

You can call printf directly within the template and specify the desired format string.

4. Custom Function

Register a custom function that wraps the printf call with the desired format string. This avoids repeating the format string in the template.

Example:

Using the custom function approach in a Gin-Gonic backend:

func main() {
    router := gin.Default()
    router.GET("/", func(c *gin.Context) {
        data := map[string]interface{}{
            "n0": 3.1415,
            "n1": "%.2f", // Format string
        }
        c.HTML(http.StatusOK, "index.html", data)
    })
    router.Run()
}

In index.html:

Number: {{printf n1 n0}}

This will format the n0 float to 2 decimal places.

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