var link = " http://www.google.com";

<a href='link' />

var link = "http://www.google.com/";
var linktext = "Google";

document.write("<a href="" + link + "">" + linktext + "</a>";

var link = "http://www.google.com/";
var linktext = "Google";

document.write("<a href="" + link + "">" + linktext + "</a>";

var link = "http://www.google.com/";
var linktext = "Google";

document.write("<a href="" + link + "">" + linktext + "</a>";

var link = "http://www.google.com";
$("a[href='link']").attr("href", link);

var anchor = document.createElement("a");
anchor.href = link;