Express JS proxy to call web api

I have the following code. And a web api which returns string array,

const express = require('express');
const proxy = require('express-http-proxy');


var app = express();

app.use('/proxy', proxy('http://localhost:56660/api/values'));

app.listen(3000);

When I tried to do localhost:3000/proxy I do not get a response, But when I use app.use('/proxy', proxy('www.google.com')); , it redirects to google web site.

Please suggest me a best approach/solution: I want to create a proxy server which gets url from browser (Application), modify the url, call the new url and send the response back to browser(Application).

You can get the URL to be proxied as a query parameter, modify it and then pass that URL to proxy, like this (use instead of app.use('/proxy', proxy('http://localhost:56660/api/values'));):

app.get('/proxy', (req, res, next) => {
    const modifiedURL = modifyURL(req.query.url)
    return proxy(modifiedURL)(req, res, next)
})

You can call you server with an URL like this (GET method):

https://my.server.com/proxy?url=https://urltobeproxied.com

UPDATE:

I think this would work according to your needs:

app.use('/proxy', (req, res, next) => {
    const requestedUrl = `${req.protocol}://${req.get('Host')}${req.url}`
    const modifiedURL = modifyURL(requestedUrl)
    proxy(modifiedURL)(req, res, next)
})

UPDATE2:

app.use('/proxy', proxy('http://localhost:56660/api/values', {
  proxyReqPathResolver: function(req) {
    const requestedUrl = `${req.protocol}://${req.get('Host')}${req.url}`
    const modifiedURL = modifyURL(requestedUrl)
    return require('url').parse(modifiedURL).path;
  }
}))

UPDATE3:

An example of proxy modifying the response (extracted from the package docs);

app.use('/proxy', proxy('http://localhost:56660/api/values', {
  userResDecorator: function(proxyRes, proxyResData, userReq, userRes) {
    data = JSON.parse(proxyResData.toString('utf8'));
    data.newProperty = 'exciting data';
    return JSON.stringify(data);
  }
}))