Why can't connect to PostgreSQL on node js?

Question

PostgreSQL

There are controllers in a separate file, the post should display data from the database. displays order-1 and order-2 as needed, but from the database there is an error in the console.

/* POST home page. */
router.post('/', function(req, res, next) {
  if (req.body.action === "order-1")
    res.send("order-1");
  else if(req.body.action === "order-2")
    res.send("order-2");

  //connect
  pg.connect(connect, function(err, client, done) {
    if(err) {
      return console.log('error fetching client from pool', err);
    }
    client.query('SELECT * FROM orders', function(err, result) {
      if(err) {
        return console.error('error running query', err);
      }
      console.log(result.rows['name']);
      done();
    });
  });
});

And here is the main file in which the path to the database

var pg = require('pg');

//DB connect
var connect = "postgres://andrey:[email protected]:5432/bytik-life";

var index = require('./routes/index');

(I also attached the connection of routers. There are post and get requests in them.)
So, for writing syntax errors 0, but writes out the error
"

Error: Can't set headers after they are sent.
    at ServerResponse.OutgoingMessage.setHeader (_http_outgoing.js:356:11)
    at ServerResponse.header (C:\Users\artys\Documents\GitHub\boutique-life\node_modules\express\lib\response.js:719:10)
    at ServerResponse.send (C:\Users\artys\Documents\GitHub\boutique-life\node_modules\express\lib\response.js:164:12)
    at done (C:\Users\artys\Documents\GitHub\boutique-life\node_modules\express\lib\response.js:956:10)
    at Object.exports.renderFile (C:\Users\artys\Documents\GitHub\boutique-life\node_modules\jade\lib\index.js:374:12)
    at View.exports.__express [as engine] (C:\Users\artys\Documents\GitHub\boutique-life\node_modules\jade\lib\index.js:417:11)
    at View.render (C:\Users\artys\Documents\GitHub\boutique-life\node_modules\express\lib\view.js:126:8)
    at tryRender (C:\Users\artys\Documents\GitHub\boutique-life\node_modules\express\lib\application.js:639:10)
    at EventEmitter.render (C:\Users\artys\Documents\GitHub\boutique-life\node_modules\express\lib\application.js:591:3)
    at ServerResponse.render (C:\Users\artys\Documents\GitHub\boutique-life\node_modules\express\lib\response.js:960:7)

"

Answer 1

res.send can only be called once. When you try to send something else, just such an error occurs, which essentially says that the answer has already been sent.