How can I send one alert from my Node.JS to my Javascript client? - Stack Overflow

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I'm doing a basic login from my node.js with mysql.

In my code example, if the session is correct send me to an html page called "home", but for this case, I need that once you make the session, my Javascript client sends an alert that says you have logged in or if its user is incorrect. And if it is correct, save the word "correct" in a variable that I can later use in my javascript file

How could I send that execution, so that my javascript file sends an alert?

app.post('/auth', function(request, response) {
var username = request.body.username;
var password = request.body.password;
if (username && password) {
    connection.query('SELECT * FROM accounts WHERE username = ? AND password = ?', 
        [username, password], function(error, results, fields) {
        if (results.length > 0) {
            request.session.loggedin = true;
            request.session.username = username;
            response.redirect('/home'); //Here I want to change the instruction so that my javascript file sends an alert and create a varible that I can use in my file Javascript
        } else {
            console.log('Incorrect Username and/or Password!');
        }           
        response.end();
    });
 });

Thanks

I'm doing a basic login from my node.js with mysql.

In my code example, if the session is correct send me to an html page called "home", but for this case, I need that once you make the session, my Javascript client sends an alert that says you have logged in or if its user is incorrect. And if it is correct, save the word "correct" in a variable that I can later use in my javascript file

How could I send that execution, so that my javascript file sends an alert?

app.post('/auth', function(request, response) {
var username = request.body.username;
var password = request.body.password;
if (username && password) {
    connection.query('SELECT * FROM accounts WHERE username = ? AND password = ?', 
        [username, password], function(error, results, fields) {
        if (results.length > 0) {
            request.session.loggedin = true;
            request.session.username = username;
            response.redirect('/home'); //Here I want to change the instruction so that my javascript file sends an alert and create a varible that I can use in my file Javascript
        } else {
            console.log('Incorrect Username and/or Password!');
        }           
        response.end();
    });
 });

Thanks

• javascript
• node.js

Share Improve this question Follow asked Dec 26, 2018 at 17:28 Isaac AlejandroIsaac Alejandro 24711 gold badge44 silver badges88 bronze badges 8

• are you using a template engine ? – Chiller Commented Dec 26, 2018 at 17:36
• @Chiller no, how can I use that? – Isaac Alejandro Commented Dec 26, 2018 at 17:37
• response.json({message: "your message goes here", status: 200 //4XX for any error}) then in javascript (front-end) you will get in then or catch based on your response. – Shailesh Rathod Commented Dec 26, 2018 at 17:42
• @ShaileshRathod, Do you have any example? – Isaac Alejandro Commented Dec 26, 2018 at 21:31
• @IsaacAlejandro How do you manage your front-end, do you use any framework, or just send static html files by NodeJS? – Slawomir Wozniak Commented Dec 26, 2018 at 21:47

 |  Show 3 more ments

3 Answers 3

Sorted by: Reset to default 3

Here's a dirty trick you can use,but it will re-render the ejs view:

On server end(using express):

app.get('/route', function (req, res) {
    res.render('view', { errormessage: 'your message' });
});

On client side(using ejs templates):

1.create an invisible div on your ejs template ,to access your ejs variable sent by server:

HTML:

  <div id='status' class='invisible'><%= errormessage %></div>

CSS:

.invisible {
display: none;
visibility: hidden;
   }

2.add this js script(jquery) at end of ejs to access this variable and create an alert:

<script>
      if($('div#status').text()!='')
      {
                alert($('div#status').text());
      }
</script>

At server side(Express middleware):

if(userNotExist) return res.status(401).end('Incorrect Username and/or Password!');

Handle at Client side.

Angular:-

$http().....
.error(function(data, status) {
  console.error('Repos error', status, data);//"Repos error" 500 "User already exists."
});

jQuery:-

$.ajax({
    type: "post",
    url: url,
    success: function (data, text) {
        //success code here.
    },
    error: function (request, status, error) {
        //error handling here.
    }
});

There is no way to directly execute code on client side, by sending a directive from the server. What you want to do, is to send an information, and interpret it properly on the client.

For instance, you can use sessions

if (results.length > 0) {
     request.session.loggedin = true;
     request.session.username = username;
     request.session.makeAlert = true;
     response.redirect('/home');
}

In the /home route

app.get('/home', function(req, res){
    const dataYouSend = {};
    if (req.session.makeAlert) dataYouSend.makeAlert = true;
    res.send(dataYouSend);
});

And finally in the JS code on /home route, use your data

fetch('adress/to/your/home')
.then(response => {
     // It may not be precisely this, I don't know how you send data
  if (response.makeAlert) alert("Alert!!!");
})
.catch(err => {
    if(err) console.log(err);
});

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