Reloading of backbone.js page causes router to not work

Question

I am using default route with a parameter and have set the pushState: true However when I refresh the page I get error in the route.

Error response

Error code 404.

following is the code:

var Backbone = require('backbone'),
SellerProfileView = require('./views/seller/SellerProfileView');

var Router = Backbone.Router.extend({
    routes: {
        ":user_name" : "sellerProfile"
    },
    sellerProfile: function (username) {
        "use strict";
        var sellerProfile = new SellerProfileView({username: username});
    }
});

module.exports = Router


var Router = require('./router'),
    Backbone = require('backbone'),
    $ = require('jquery');

var app = {
    init: function () {
        "use strict";
        Backbone.$ = $;
        this.router = new Router();
        $(document).ready(function () {
            Backbone.history.start({ pushState: true, route: '/' });
        });
    }
};

module.exports = app;
app.init();