Iron-Router waitOn()

routing.js

// Wait On one or more subscription before loading the page.
Router.route("/", {
    name: "home",
    waitOn: function () {
        return [
          Meteor.subscribe('users'),
          // any other subscription to wait on
        ];
    },
    action: function () {
        if (this.ready()) {
            // Send user to sign in form, if not logged in
            if (!Meteor.userId()) {
                Router.go("/sign_in");
            } else {
                this.render("home");
            }
        }
    }
});