Do an ajax call to server.js from a vue app, using heroku

I have followed this tutorial with success :

https://medium.com/p/a69845ace489/responses/show

Now, how can I do an ajax call from my dist directory using vue axios, to my server.js node file ?

Because heroku is giving randoms ports to my connexion with process.env.PORT.

This is my server config in main.js, inside the vue.js app, inside the dist directory :

Vue.server = Vue.prototype.server = "https://myapp.herokuapp.com/";

Please notice that there is no port, cause i can't know which port is used by heroku.

This is an axios random call, from the vue.js app

axios.post(Vue.server + "getUser", {id: this.id})
    .then(response => {
        this.user = response.data;
    })
    .catch(function (erreur) {
        console.log(erreur);
    });

This is my server.js file :

// server.js
var express = require('express');
var path = require('path');
var serveStatic = require('serve-static');
app = express();
app.use(serveStatic(__dirname + "/dist"));
var port = process.env.PORT || 5000;
app.listen(port);console.log('server started '+ port);

My problem is that the port cant be set in my vue app, all of the rest of the code is working, i dont include the node rest stuff.

Do you think that keeping localhost as a Vue.server variable would work online ? Thank you

PART 2 :

Changed my server.js file like this , added a getUsers post web service :

// server.js
var express = require('express');
var path = require('path');
var serveStatic = require('serve-static');
const mongodb = require("mongodb");
app = express();
app.use(serveStatic(__dirname + "/dist"));
var port = process.env.PORT || 80;

const cors = require("cors");

app.use(cors());

app.post("/getUsers", function(req, res) {
   res.send('ok');
});

app.listen(port);
console.log('server started '+ port);

2. This is my Helloworld.vue now :

   import axios from "axios";
   axios.defaults.withCredentials = true;
   export default {
     name: 'HelloWorld',
     props: {
       msg: String
     },methods: {
       getUsers: function () {
   
               axios
                   .post("http://localhost/" + "getUsers", {
                   })
                   .then(response => {
                      console.log(response);
                   })
                   .catch(function (error) {
                       console.log(error);
                   });
           }
           },
       created: function () {
           this.getUsers();
   
       }
   }
   </script>
   

2.5 : on my localhost server, all is working well, the ajax call is working with no CORS error at all :

node server.js 

3. Uploading this to HEROKU :

git push heroku master

4. This is the error :

Cross-Origin Request Blocked: The Same Origin Policy disallows reading the remote resource at http://localhost/getUsers. (Reason: CORS request did not succeed).