urlJoin() {
    const paths = Array.prototype.slice.call(arguments);
    const url2 = "/" + paths.map(function(e) {
      return e.replace(/^\/|\/$/g, "");
    }).filter(function(e) {
      return e;
    }).join("/");
    return url2.replace("//", "/");
  }
Joins all arguments as a URL string
see http://stackoverflow.com/a/28592528/3016654
since v1.0.10, fixed potential double // issue
arguments {string} URL fragments
@returns {string} _