I've come across the following JavaScript code snippet in O'Reilly's JavaScript Web Applications:
// helper.js
var helper = {};
helper.formatDate = function(){ /* ... */ };
// template.html
<div>
${ helper.formatDate(this.date) }
</div>
However no reference to any particular JavaScript library is provided here. What is the likely meaning of the ${ ... } syntax and how does it work? Does this come from the use of any particular library? I've seen jQuery's $() notation where $ is a function but I've not seen $ followed by a curly bracket pair anywhere.
Thanks.