How to Prevent a Trailing Comma in Go Template Array Output?

Detect Last Item in an Array Using Range in Go Templates

In a Go template, you might encounter a situation where you need to print an array without a trailing comma after the last item.

Consider the following code:

<code class="go">package main

import "os"
import "text/template"

func main() {
    params := map[string]interface{}{
        "items": [3]int{1, 4, 2},
    }
    tpl := "{{range $i, $el := .items}}{{$el}},{{end}}"
    lister, _ := template.New("foo").Parse(tpl)
    lister.Execute(os.Stdout, params)
}</code>

This code outputs:

1,4,2,

To remove the trailing comma, you can modify the template to:

<code class="go">tpl := "{{range $i, $el := .items}}{{if $i}},{{end}}{{$el}}{{end}}."</code>

The critical change here is the introduction of the conditional statement {{if $i}},{{end}} inside the range loop. Let's break down what this does:

• {{range $i, $el := .items}}: This line initiates a loop over the items array, where $i represents the index and $el represents the current item.
• {{if $i}},{{end}}: Inside the loop, this conditional checks whether it's not the first item in the array. If it's not the first item ($i is not 0), it prints a comma.
• {{.el}}: This part prints the current item in the array.
• {{end}}: This line ends the loop.
• . at the end of the template: Finally, we add a period (".") to the end of the template to terminate the output.

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