https://medium.com/@mobilpadde/create-a-reverse-url-shortner-9d03ac5d73b5

1.js

const express = require("express");
const app = express();

app.get("/", (req, res) => {
    res.render("index.pug");
});

app.listen(3000);

10.js

// ...

module.exports = (uri => {
  return new Promise((resolve, reject) => {
        rp({
            uri: uri,
            followAllRedirects: true,
            resolveWithFullResponse: true
        }).then(res => {
            resolve(res.request.uri.href);
        }).catch(reject);
    });
});

// ...

11.js

const express = require("express");
const check = require("./lib/checker.js");
const app = express();

// ...

2.js

// ...
const app = express();

app.set("view engine", "pug");
app.set("views", __dirname + "/views");

// ...

3.pug

html
    head
        link(href="/main.css", rel="stylesheet")
    body
        #wrapper
            input#url(type="text")
            button#go Go Figure
            h1#result
        script(src="main.js")

4.css

*{
    margin: 0;
    padding: 0;
    outline: none;
}

body{
    font: 14px/1.1 sans-serif;
    margin: 0 auto
}

#wrapper{
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    text-align: center;
}

#url, #go{
    padding: 5px;
    font-size: 2em;
    border: none;
    border-bottom: 2px solid #c9f1f1;
}

#go{
    background: transparent;
    border-radius: 2px 2px 0 2px;
    transition: background 250ms ease-in;
}

#go:hover{
    background: rgba(201, 241, 241, 0.35);
}

#result{
    padding: 15px;
}

5.js

"use strict"

window.addEventListener("load", () => {
    const url = document.getElementById("url");
    const btn = document.getElementById("go");

    const res = document.getElementById("result");
});

6.js

// ...

const res = document.getElementById("result");

btn.addEventListener("click", () => {
    fetch("/check/" + url.value, {
        method: "post"
    })
    .then(result => result.json())
    .then(uri => res.innerText = uri);
});

// ...

7.js

// ...
app.get("/", (req, res) => {
    res.render("index.pug");
});

app.post("/check/:url(*)", (req, res) => {
    check(req.params.url).then(result => {
        res.json(result);
    });
});

// ...

8.js

const rp = require("request-promise");
const Promise = require("bluebird");

9.js

// ...
const Promise = require("bluebird");

module.exports = (uri => {
    
});