This is something I fiddled with during development. A really helpful thing if we need to wrap strings around array items.
var values = [1, 3, 3, 7];
var open = '<span>';
var close = '</span>';
var html = open + values.join(close + open) + close;
console.log(html); // => "<span>1</span><span>3</span><span>3</span><span>7</span>"