var t = 0;
var p = /^[a-z0-9A-Z_-]*@$/ + t.toString();

p.test("asdf2@0");

var t = 0;
var re = new RegExp("^/\[a-z0-9A-Z_-]*@" + t.toString() + "/\$");
var z = re.test("asdf2@0");