How to reuse matched value of regex in replace JS function

replace_regex.js

var text = "this is a {highlighted} text"; 

var regex = /\{\S+?\}/g;
var html = text.replace(regex, '<mark>$&</mark>'); // $& = matched value = {highlight}
alert(html); // => "this is a <mark>{highlighted}</mark> text"

var regex2 = /\{(\S+?)\}/g; // you need ()-brackets to get $1
var html2 = text.replace(regex2, '<mark>$1</mark>'); // $1 = first () = highlight
alert(html2); // => "this is a <mark>highlighted</mark> text"