How to Repeat an HTML Line N Times in Go Web Applications?

Repeating an HTML Line N Times in Go Web Applications

In the context of web development, it can be useful to iterate over HTML content a specified number of times. For example, when creating pagination links or generating dynamic lists. Go provides several ways to achieve this through HTML templates.

Using the {{range}} Action

Go templates offer the {{range}} action, which enables iterating over a slice, array, or map. To use this for repeating HTML content, you need to provide a collection of items that represent the desired repetitions.

Passing a Zero-Value Slice

One approach is to pass an empty slice. Go will create a slice with no elements at runtime. In our example, we can pass a zero-value slice of structs: make([]struct{}, n).

For instance, let's consider the following HTML code:

<ul>
    <li><a href="/?page=1">1</a></li>
    <li><a href="/?page=2">2</a></li>
                      .
                      .
                      .
    <li><a href="/?page=n">n</a></li>
</ul>

We can use the {{range}} action to iterate over a zero-value slice, fill the links with incrementing values, and generate the HTML dynamically.

The Go template code could look like this:

const templ = `
<ul>
{{range $idx, $e := .}}
    <li><a href="/?page={{$idx}}">{{idx}}</a></li>
{{end}}
</ul>`

Using a Filled Slice

Another option is to explicitly fill a slice with the desired values. This can be useful when you need more control over the generated content. For example, to generate odd numbers starting with 2, you can create a filled slice:

values := make([]int, n)
for i := range values {
    values[i] = (i + 1) * 2
}

And modify the template to use the slice elements directly:

const templ = `
<ul>
{{range .}}
    <li><a href="/?page={{.}}">{{}}</a></li>
{{end}}
</ul>`

Using a Zero-Value Slice and Custom Function

If you only need increasing numbers starting from 1, you can register a custom function to add 1 to the index of the zero-value slice:

func Add(i int) int { return i + 1 }

tmpl := template.Must(template.New("").Funcs(template.FuncMap{
    "Add": Add,
}).Parse(templ))

Then modify the template to call the custom function:

const templ = `
<ul>
{{range $idx, $e := .}}{{$idx := Add $idx}}
    <li><a href="/?page={{$idx}}">{{idx}}</a></li>
{{end}}
</ul>`

By utilizing these techniques, you can efficiently generate repetitive HTML content in your Go web applications.

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