display soy variable value like alert in javascript

Question

Do we have anything equivalent to javascript alert() in soy file to display variable values?

I tried using javascript also in soy like below but didnt help (extendedFieldView is a List):

<#assign extendedField = extendedFieldView.ExtendedField>
<script type="text/javascript">   
alert("${extendedField}")
</script>

Thanks!