jQuery - Append a Value to a INPUT, keeping it a Comma Delimited list -

i have input follows:

<input type="hidden" id="attachment-uuids" value=""> 

i'd able append value input, @ different times:

$('#attachment-uuids).val('55555'); 

results in:

<input type="hidden" id="attachment-uuids" value="55555"> 

but doing:

$('#attachment-uuids).val('66666'); 

results in:

<input type="hidden" id="attachment-uuids" value="66666"> 

where i'd following:

<input type="hidden" id="attachment-uuids" value="55555, 66666"> 

how can append values when value empty , when value not empty comma delimited list?

thanks

$('#attachment-uuids').val(function(i,val) {       return val + (!val ? '' : ', ') + '66666'; }); 

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edit: @mkoryak noted, i'm doing unnecessary negation of val in conditional operator. rewritten without ! as:

(val ? ', ' : '')