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Using range to Iterate over an Array

Sam Xiao's Avatar 2022-01-19

The Go Templates make heavy use of range to iterate over a Map, Array, or Slice.

Version

Hugo 0.92

Using Context

overview000

Using range to iterate over an Array to render <li>.

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <script src="alpine.js" defer></script>
    <link rel="stylesheet" href="output.css" />
    {{ $numbers := slice 1 2 3 }}
  </head>
  <body>
    <ul class="ml-6 list-disc">
      {{ range $numbers }}
      <li>{{ . }}</li>
      {{ end }}
    </ul>
  </body>
</html>

Line 8

{{ $numbers := slice 1 2 3 }}
  • slice : define an Array with [1, 2, 3]

Line 11

<ul class="ml-6 list-disc">
  {{ range $numbers }}
  <li>{{ . }}</li>
  {{ end }}
</ul>
  • range : pass Array directly to range. The . represents an element in Array

Declaring Variable

overview000

Same result but using a variable with range.

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <script src="alpine.js" defer></script>
    <link rel="stylesheet" href="output.css" />
    {{ $numbers := slice 1 2 3 }}
  </head>
  <body>
    <ul class="ml-6 list-disc">
      {{ range $x := $numbers }}
      <li>{{ $x }}</li>
      {{ end }}
    </ul>
  </body>
</html>

Line 12

{{ range $x := $numbers }}
<li>{{ $x }}</li>
{{ end }}
  • range : declare a variable for Array element

Declaring Index

overview001

Using range to iterate over Array with index.

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <script src="alpine.js" defer></script>
    <link rel="stylesheet" href="output.css" />
    {{ $numbers := slice 1 2 3 }}
  </head>
  <body>
    <ul class="ml-6 list-disc">
      {{ range $i, $x := $numbers }}
      <li>{{ $i }}: {{ $x }}</li>
      {{ end }}
    </ul>
  </body>
</html>

Line 12

{{ range $i, $x := $numbers }}
<li>{{ $i }}: {{ $x }}</li>
{{ end }}
  • range : first declared variable will map to each element’s index

Empty Array

overview002

We can also define how to deal with an empty Array.

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <script src="alpine.js" defer></script>
    <link rel="stylesheet" href="output.css" />
    {{ $numbers := slice }}
  </head>
  <body>
    <ul class="ml-6 list-disc">
      {{ range $numbers }}
      <li>{{ . }}</li>
      {{ else }}
      <li>N/A</li>
      {{ end }}
    </ul>
  </body>
</html>

Line 12

{{ range $numbers }}
<li>{{ . }}</li>
{{ else }}
<li>N/A</li>
{{ end }}
  • else : If the Array passed into the range is zero-length then the else statement is evaluated

Conclusion

  • range also support index and empty Array with else

Reference

Hugo, Iteration

# Hugo