315
votes

I am using express to make a web app in node.js. This is a simplification of what I have:

var express = require('express');
var jade = require('jade');
var http = require("http");


var app = express();
var server = http.createServer(app);

app.get('/', function(req, res) {
    // Prepare the context
    res.render('home.jade', context);
});

app.post('/category', function(req, res) {
    // Process the data received in req.body
    res.redirect('/');
});

My problem is the following:

If I find that the data sent in /category doesn't validate, I would like pass some additional context to the / page. How could I do this? Redirect doesn't seem to allow any kind of extra parameter.

9
Check out express' flash: stackoverflow.com/questions/12442716/… - tymeJV
Terminology matters here: there is no / page. There is a / route, which express can service, and there is a homepage template, which express can render. If you want to preserve some data for rendering the homepage template after a redirect, the accepted answer notwithstanding, sessions are your friend. They give you a data store that persists across requests and responses for individual browsing users so you can put data in during /category handling, and then take it out if it's there during / handing. - Mike 'Pomax' Kamermans

9 Answers

433
votes

There are a few ways of passing data around to different routes. The most correct answer is, of course, query strings. You'll need to ensure that the values are properly encodeURIComponent and decodeURIComponent.

app.get('/category', function(req, res) {
  var string = encodeURIComponent('something that would break');
  res.redirect('/?valid=' + string);
});

You can snag that in your other route by getting the parameters sent by using req.query.

app.get('/', function(req, res) {
  var passedVariable = req.query.valid;
  // Do something with variable
});

For more dynamic way you can use the url core module to generate the query string for you:

const url = require('url');    
app.get('/category', function(req, res) {
    res.redirect(url.format({
       pathname:"/",
       query: {
          "a": 1,
          "b": 2,
          "valid":"your string here"
        }
     }));
 });

So if you want to redirect all req query string variables you can simply do

res.redirect(url.format({
       pathname:"/",
       query:req.query,
     });
 });

And if you are using Node >= 7.x you can also use the querystring core module

const querystring = require('querystring');    
app.get('/category', function(req, res) {
      const query = querystring.stringify({
          "a": 1,
          "b": 2,
          "valid":"your string here"
      });
      res.redirect('/?' + query);
 });

Another way of doing it is by setting something up in the session. You can read how to set it up here, but to set and access variables is something like this:

app.get('/category', function(req, res) {
  req.session.valid = true;
  res.redirect('/');
});

And later on after the redirect...

app.get('/', function(req, res) {
  var passedVariable = req.session.valid;
  req.session.valid = null; // resets session variable
  // Do something
});

There is also the option of using an old feature of Express, req.flash. Doing so in newer versions of Express will require you to use another library. Essentially it allows you to set up variables that will show up and reset the next time you go to a page. It's handy for showing errors to users, but again it's been removed by default. EDIT: Found a library that adds this functionality.

Hopefully that will give you a general idea how to pass information around in an Express application.

48
votes

The easiest way I have found to pass data between routeHandlers to use next() no need to mess with redirect or sessions. Optionally you could just call your homeCtrl(req,res) instead of next() and just pass the req and res

var express  = require('express');
var jade     = require('jade');
var http     = require("http");


var app    = express();
var server = http.createServer(app);

/////////////
// Routing //
/////////////

// Move route middleware into named
// functions
function homeCtrl(req, res) {

    // Prepare the context
    var context = req.dataProcessed;
    res.render('home.jade', context);
}

function categoryCtrl(req, res, next) {

    // Process the data received in req.body
    // instead of res.redirect('/');
    req.dataProcessed = somethingYouDid;
    return next();
    // optionally - Same effect
    // accept no need to define homeCtrl
    // as the last piece of middleware
    // return homeCtrl(req, res, next);
}

app.get('/', homeCtrl);

app.post('/category', categoryCtrl, homeCtrl);
15
votes

I had to find another solution because none of the provided solutions actually met my requirements, for the following reasons:

  • Query strings: You may not want to use query strings because the URLs could be shared by your users, and sometimes the query parameters do not make sense for a different user. For example, an error such as ?error=sessionExpired should never be displayed to another user by accident.

  • req.session: You may not want to use req.session because you need the express-session dependency for this, which includes setting up a session store (such as MongoDB), which you may not need at all, or maybe you are already using a custom session store solution.

  • next(): You may not want to use next() or next("router") because this essentially just renders your new page under the original URL, it's not really a redirect to the new URL, more like a forward/rewrite, which may not be acceptable.

So this is my fourth solution that doesn't suffer from any of the previous issues. Basically it involves using a temporary cookie, for which you will have to first install cookie-parser. Obviously this means it will only work where cookies are enabled, and with a limited amount of data.

Implementation example:

var cookieParser = require("cookie-parser");

app.use(cookieParser());

app.get("/", function(req, res) {
    var context = req.cookies["context"];
    res.clearCookie("context", { httpOnly: true });
    res.render("home.jade", context); // Here context is just a string, you will have to provide a valid context for your template engine
});

app.post("/category", function(req, res) {
    res.cookie("context", "myContext", { httpOnly: true });
    res.redirect("/");
}
10
votes

use app.set & app.get

Setting data

router.get(
  "/facebook/callback",
  passport.authenticate("facebook"),
  (req, res) => {
    req.app.set('user', res.req.user)
    return res.redirect("/sign");
  }
);

Getting data

router.get("/sign", (req, res) => {
  console.log('sign', req.app.get('user'))
});

6
votes

Here s what I suggest without using any other dependency , just node and express, use app.locals, here s an example :

    app.get("/", function(req, res) {
        var context = req.app.locals.specialContext;
        req.app.locals.specialContext = null;
        res.render("home.jade", context); 
        // or if you are using ejs
        res.render("home", {context: context}); 
    });

    function middleware(req, res, next) {
        req.app.locals.specialContext = * your context goes here *
        res.redirect("/");
    }
4
votes

we can use express-session to send the required data

when you initialise the app

const express = require('express');
const app = express();
const session = require('express-session');
app.use(session({secret: 'mySecret', resave: false, saveUninitialized: false}));

so before redirection just save the context for the session

app.post('/category', function(req, res) {
    // add your context here 
req.session.context ='your context here' ;
    res.redirect('/');
});

Now you can get the context anywhere for the session. it can get just by req.session.context

app.get('/', function(req, res) {

    // So prepare the context
var context=req.session.context;
    res.render('home.jade', context);
});
3
votes

You can pass small bits of key/value pair data via the query string:

res.redirect('/?error=denied');

And javascript on the home page can access that and adjust its behavior accordingly.

Note that if you don't mind /category staying as the URL in the browser address bar, you can just render directly instead of redirecting. IMHO many times people use redirects because older web frameworks made directly responding difficult, but it's easy in express:

app.post('/category', function(req, res) {

  // Process the data received in req.body

  res.render('home.jade', {error: 'denied'});
});

As @Dropped.on.Caprica commented, using AJAX eliminates the URL changing concern.

0
votes

I use a very simple but efficient technique in my app.js ( my entry point ) I define a variable like

let authUser = {};

Then I assign to it from my route page ( like after successful login )

authUser = matchedUser

It May be not the best approach but it fits my needs.

-2
votes
 app.get('/category', function(req, res) {
  var string = query
  res.redirect('/?valid=' + string);
});

in the ejs you can directly use valid:

<% var k = valid %>