Node.js http server, function can't access response object

Question

I have the following http server code

var server = http.createServer(function (req, response) {
    body = "";
    req.on("data", function (data) {
    body += data;
  });
  req.on("end", function (){
    parseRequest(body);
  });
}).listen(8080);

var parseRequest = function (data) {
  try {
    jsonData = JSON.parse(data);
    handleRequest(jsonData);
  }
  catch (e) {
    console.log("Json Parse Failed")
    console.log(e);
    response.writeHead(500);
    response.end("Json Parse Failed");
  }
}

I thought that the parseRequest function should be able to access it's variables in in its parent function's scope. Is there something I am doing wrong here?

The error I get is,

response.writeHead(500);
^
ReferenceError: response is not defined

Variable declared inside the scope of a function are limited to that scope unless declare globally. so you need parseRequest inside the same scope as response if you want it to use response. — GillesC
– GillesC, Commented Jun 25, 2015 at 6:19
"access it's variables in in its parent function's scope" - yes, it does. Only the scope of the createServer callback is not the parent scope of parseRequest. Move it inside there and it would work. — Bergi
– Bergi, Commented Jun 25, 2015 at 6:27
Btw, you are missing variable declarations for body and jsonData. Please use strict mode to avoid such accidental globals. — Bergi
– Bergi, Commented Jun 25, 2015 at 6:32

Sebastian Nette · Accepted Answer · 2015-06-25 06:19:24Z

1

Change it to:

req.on("end", function (){
    parseRequest(response, body);
});

And then:

var parseRequest = function (response, data) { ...

And now you can access response. ;)

answered Jun 25, 2015 at 6:19

Sebastian Nette

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9 Comments

user4062487 Over a year ago

I know I could do this, but it seems inefficient.

Sebastian Nette Over a year ago

What is inefficient about this?

Joel Over a year ago

Inefficient? If you don't propagate the variables you need to your method scope, you have no chance to access them.

user4062487 Over a year ago

I checked, this worked in the chrome js console,a = function(b){x=b;d()};d = function(){console.log(x)};a("hi"); prints hi.

Joel Over a year ago

Because in this example, it's declared in the scope enclosing your function

|

Bergi · Accepted Answer · 2015-06-25 06:30:44Z

0

Try this:

var server = http.createServer(function (req, response) {
  var body = "";
  req.on("data", function (data) {
    body += data;
  });
  var parseRequest = function (data) {
    try {
       var jsonData = JSON.parse(data);
       handleRequest(jsonData);
    } catch (e) {
      console.log("Json Parse Failed")
      console.log(e);
      response.writeHead(500);
      response.end("Json Parse Failed");
    }
  };
  req.on("end", function (){
    parseRequest(body);
  });
}).listen(8080);

edited Jun 25, 2015 at 6:30

Bergi

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answered Jun 25, 2015 at 6:19

KennyXu

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2 Comments

Sebastian Nette Over a year ago

Why would you create a new function per request if there is no need for it?

Bergi Over a year ago

@SebastianNette: Now he's creating 3 instead of 2 functions per request. Doesn't seem to be a large difference.

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