ReactJS ExpressJS-Ajax表单

Question

Due to my starting level with React and Node/Express and, above all, time restriction, I'm developing a single page application without database, so I have only static pages.

I've configured react-router to have clear url, using the hash (http://localhost:8080/#/contacts) i avoid also server calls:

let history = createHistory({
  queryKey: false
});

I've the necessity to send mail from my form. To do this i've find nodemailer and i need to invoke it from an ajax call. Just to do some pratique with React i've configured my ajax call in my componentDidMount function:

openForm() {
    $('#contacts-form').on('submit', function(){
        $.ajax({
            url: '/mail',
            type: 'post',
            data: { msg: $('#data').val() },
            success: function(data){
                console.log(data);
            },
            error: function(){
                console.log('err form');
            }
        });
        return false;
    });
}

componentDidMount() {
    this.openForm();
}

Now, after I've installed body-parser and set my form's action to "/mail", in my server.js I've configured my .post route

app.use( bodyParser.json() );
app.use(bodyParser.urlencoded({
  extended: true
}));

app.post('/mail', function(req, res){
    res.send('ajax call recived');
});

So now once I try to submit my form, my ajax call fails, in console i get this error:

POST http://localhost:8080/mail 404 (Not Found)
err form

It's the first time i'm working with these tools, where i'm doing wrong?