Passing Variables from Node.js Server to Static Page Script

Question

I have a basic node.js app serving a static index.html that contains a JS app. I have a login route that validates a username/pwd against my mongo database and redirects to '/':

app.post('/login', function(req,res) {
    let inputUser=req.body.username;
    let inputPwd=req.body.password;

    findUser({'username':inputUser},function(data){
        if ((data[0].srnm===inputUser)&&(data[0].psswd===inputPwd))
        {
            res.redirect('/');
        }
        else
        {
            res.writeHead(200);
            res.write(`INVALID USERNAME OR PASSWORD TRY AGAIN OR GO AWAY`);
            res.end();
        }
    });
});

My index.html contains a script.src JS app.

app.get('/', function (req, res) {
    res.sendFile(path.join(__dirname+'/index.html')); 
});

I want to access an IS_LOGGED_IN flag in this script.

How do I pass the script this information? Do I need to do an AJAX request / put it in a header before my redirect somehow? Or is my approach somehow flawed? Sorry if this is blatantly obvious. I'm very new to node (and also need to learn async.js/promises to avoid callback hell). Thanks.

Hitmands · Accepted Answer · 2021-01-25 09:05:49Z

3

A good approach is using a Template Engine instead of serving a pure .html file, so:

Managing the Index Route:

Install a Basic Template Engine npm install ejs --save
Use it as Express Template Engine app.set('view engine', 'ejs')
Set the views path app.set('views', path.join(__dirname, 'views'));
Render app.get('/'. (req, res) => res.render('Index', {IS_LOGGED: true });
Index.ejs <script>window.INITIAL_STATE = {IS_LOGGED: <%- IS_LOGGED %>}; </script>

Managing the Login API:

Instead of res.write(200); ...INVALID USERNAME..., respond with a more consistent status code so your client can understand when a login request is done.

app.get('/login', (req, res) => res.status(401).end());

edited Jan 25, 2021 at 9:05

answered Jan 13, 2017 at 19:08

Hitmands

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Comments

Med Lazhari · Accepted Answer · 2017-01-13 18:57:19Z

0

You can use Ajax script then you should pass a JSON response

res.send({IS_LOGGED_IN: true})

Or past your flag as a flash session using express-flash module (https://www.npmjs.com/package/express-flash)

Example

req.flash('IS_LOGGED_IN', true);

On html page render you get your flag by:

app.get(function(req, res, next){
    return res.render('index.html', {
        IS_LOGGED_IN: req.flash('IS_LOGGED_IN'),
    });
});

answered Jan 13, 2017 at 18:57

Med Lazhari

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Comments

David Jones · Accepted Answer · 2017-01-13 19:05:19Z

If all you want to do is indicate to your on-page script that a user is logged in, the easiest way would be to set a cookie in the log on script.

res.cookie('loggedIn', 'true')

Then access it from within your script.

<script type="text/javascript">
        function setCookie(key, value) {
            var expires = new Date();
            expires.setTime(expires.getTime() + (1 * 24 * 60 * 60 * 1000));
            document.cookie = key + '=' + value + ';expires=' + expires.toUTCString();
        }

        function getCookie(key) {
            var keyValue = document.cookie.match('(^|;) ?' + key + '=([^;]*)(;|$)');
            return keyValue ? keyValue[2] : null;
        }

    if (getCookie('loggedIn')) {
        document.write('User is logged in')
    }
</script>

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