var t1 = "mail";
var t2 = "to:";
var em1 = "umer.khan";
var em2 = "mail";
var em3 = ".com";
document.write("<a hr" + "ef=" + t1 + t2 + em1 + "&#64;" + em2 + em3 + ">" + em1 + "&#64;" + em2 + em3 + "</a>");