var newText = $("p").text().split(" ").join("</span> <span>");

var newText = "<span>" + $("p").text().split(" ").join("</span> <span>") + "</span>";

<p>Test is a demo.</p>

<p><span>Test</span> <span>is</span> <span>a</span> <span>demo.</span></p>

var today = new Date();
 $('#'+[today.getMonth()+1, today.getDate(), today.getFullYear()].join("_")).whatever();