PrestaShop: add javascript array elements using smarty

If I understand you well, if in PHP you assign to Smarty elements like this:

$smarty->assign('combinations', array (1,2,3,20));

you can use in Smarty:

<script>
    var combinations = [];
    {foreach $combinations as $item}
    combinations.push({$item})
    {/foreach}
    console.log(combinations);
</script>

As I added console.log(combinations); to log to JS console, in console there is

Array [ 1, 2, 3, 20 ]

so all elements were inserted into JavaScript array.

In case you have more complex PHP array:

$smarty->assign('combinations', array(
        'a' => 'aval',
        'b' => 'bval',
        'c' => array('c1' => 'c1val', 'c2' => 'c2val'),
        'd' => array(
            'd1' => 'd1val',
            'd2' => array(
                'd2‌​1' => 'd21val',
                'd22'   => 'd22val',
                'd23'   => array('d231', 'd232')
            )
        )
    ));

and you want create flat JavaScript array you may use:

{function jsadd}
    {foreach $data as $item}
        {if not $item|@is_array}
            combinations.push('{$item}')
        {else}
            {jsadd data = $item}
        {/if}
    {/foreach}
{/function}

<script>
    var combinations = [];
    {jsadd data=$combinations}
    console.log(combinations);
</script>

and you will get:

Array [ "aval", "bval", "c1val", "c2val", "d1val", "d21val", "d22val", "d231", "d232" ]

EDIT2

And if you need to create multidimensional array in JavaScript using data from PHP as you explained in comment you can use this Smarty template:

{function jsadd keypart=''}
    {foreach $data as $key => $item}
        {if not $item|@is_array}
            {if $keypart eq ''}
                combinations['{$key}'] = '{$item}'
             {else}
                combinations{$keypart}['{$key}'] = '{$item}'
            {/if}
        {else}
            combinations{$keypart}['{$key}'] = [];
            {jsadd data = $item keypart = "`$keypart`['`$key`']" }
        {/if}
    {/foreach}
{/function}

<script>
    var combinations = [];
    {jsadd data=$combinations}
    console.log(combinations['a']);
</script>