Referencing Go array in Javascript

You need to understand something:

Template actions such as {{index .Array 0}} are executed at server side in your Go application.

Javascript code is interpreted and run at client side in the browser.

The template parameter value used in template actions (Array in your example) does not exist at client side (e.g. as a Javascript object). And Javascript code is not run by the template engine. So the template parameter (value) and Javascript (execution) live in 2 different “spaces”.

Having said that, it is not possible to mix template actions/variables and Javascript execution.

You have 2 options:

1) Do what you want to do with template actions.

2) Use the template to create Javascript code which when executed at the client side will construct/recreate the array as a Javascript object so it will be available for further Javascript processing.

Note that if you just want to loop over the array once, creating a Javascript array is not neccessary, you can simply render the JavaScript code that would be the loop body inside a {{range}} template action. See Simon’s answer as an example to this.

Elaborating #1

You can use the {{range .Array}} action to loop over Array, and the block is executed for each element, pipeline set to the array element so you can output the array elements like this:

{{range .Array}}
    {{.}}
{{end}}

Of course you can put anything else inside the block, not just the array elements. You can even access the current index like this:

{{range $idx, $value := .Array}}
    Index = {{$idx}}; Element = {{$value}}<br>
{{end}}

Elaborating #2

Let’s say your Array contains int numbers, you can recreate it in Javascript and loop over it in Javascript with a template like this:

<script>
    var arr = [
        {{range .Array}}
            {{.}},
        {{end}}
    ];

    // Now you have a javascript array: arr, loop over it to do something:
    html = "";
    for(var i = 0; i < arr.length; i++) {
        html += " " + arr[i];
    }
</script>

Or since the template engine supports “rendering” arrays and slices as JavaScript arrays, you can simply write:

<script>
    var arr = {{.Array}};

    // Now you have a javascript array: arr, loop over it to do something:
    html = "";
    for(var i = 0; i < arr.length; i++) {
        html += " " + arr[i];
    }
</script>