NodeJS res.send not returning variable value

Question

I'm working on a NodeJS/Express program and I'm trying to get a POST request to return data. When I return a direct string, I get the correct response.

app.post("/DoStuff", function(req, res, Data) {
  DoStuf.DoStuffFunction(req.body.UserID, function(label) {
    Data = label
    })
    res.send({message: "Stuff"});
  })

When I change it to return a variable (which is still a string) it only returns "{}".

app.post("/DoStuff", function(req, res, Data) {
  DoStuf.DoStuffFunction(req.body.UserID, function(label) {
    Data = label
    })
    res.send({message: Data});
  })

Even when I make Data = "foo" the response is "{}"

Suresh Prajapati · Accepted Answer · 2018-08-17 07:21:59Z

3

You need to send from inside of callback function. In your code res.send is independent of DoStuffFunction's callback

app.post("/DoStuff", function(req, res, Data) {
  DoStuf.DoStuffFunction(req.body.UserID, function(label) {
    Data = label;
    res.send({message: Data});
    })   
  })

answered Aug 17, 2018 at 7:21

Suresh Prajapati

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Comments

Vasyl Moskalov · Accepted Answer · 2018-08-17 07:24:11Z

1

Looks like your DoStuffFunction is async. So just move res.send(..) in callback.Something like

app.post("/DoStuff", function(req, res, Data) {
  DoStuf.DoStuffFunction(req.body.UserID, function(label) {
    res.send({message: label});
   })
})

answered Aug 17, 2018 at 7:24

Vasyl Moskalov

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Comments

Sridhar · Accepted Answer · 2018-08-17 07:32:26Z

1

When I change it to return a variable (which is still a string) it only returns "{}".

This is because DoStuf.DoStuffFunction(){} is asynchronous.

The reason why it works when you use stuff as value is because the operation is synchronous. And you have value with you before sending the response.

If you want to send response only after the DoStuffFunction() completes, place the response.send() within the callback.

'use strict';

app.post("/DoStuff", function(req, res, Data) {
  DoStuf.DoStuffFunction(req.body.UserID, function(label) {
    res.send({message: label}); //you can send label's value directly
    });
});

answered Aug 17, 2018 at 7:32

Sridhar

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