Node error cannot set headers after they send

Question

Im new to nodeJs and I want to read file from the system, I was able to see the file content in the console but not in the browser and I

what am I missing here?

var myData = null;
    fs.readFile('C:\\Users\\jbt\\Desktop\\simplefile.txt', 'utf8', function (err,data) {
        if (err) {
            return console.log("the error is: " + err);
        }
        console.log(data);
        myData = data;
    });
    res.send(myData);

I try some other post in SO but nothing helps..

This question is beginning to be posted too often... always the same answer : Javascript is _asynchronous_. Same question yesterday, please read my answer : http://stackoverflow.com/questions/30636547/how-to-set-retrieve-callback-in-mongoose-in-a-global-variable/30636635#30636635 — Jeremy Thille, Jun 05 '15 at 09:40
@JeremyThille - Thanks but I dont understand how it helps me here... — John Jerrby, Jun 05 '15 at 09:45
It's just exactly the same problem and the same answer. You're sending a variable that's not been filled because the process is _asynchronous_. It's almost the same code in both questions, except in your case it's readFile instead of a SQL query. — Jeremy Thille, Jun 05 '15 at 09:50
Aside from the async issues, you're not showing us all of your code, because the code you're showing wouldn't result in the error you're getting. — robertklep, Jun 05 '15 at 10:01
possible duplicate of [How to return the response from an asynchronous call?](http://stackoverflow.com/questions/14220321/how-to-return-the-response-from-an-asynchronous-call) — Ben Fortune, Jun 05 '15 at 10:34

score 1 · Answer 1 · answered Jun 05 '15 at 10:18

1

you are trying to send the response twice ie. res.send() is being called twice that is why once the response is sent you cannot resend it.

answered Jun 05 '15 at 10:18

Aditya_Anand

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Thanks but not sure that I got it,can you please give an example ? – John Jerrby Jun 05 '15 at 11:40
Please check how many times in total are you doing the res.send in the api call? – Aditya_Anand Jun 05 '15 at 11:47

score 0 · Answer 2 · answered Jun 05 '15 at 09:34

fs.ReadFile is async operation, you are sending response back and reading file in parallel. You should do it like this

    var myData = null;
    fs.readFile('C:\\Users\\jbt\\Desktop\\simplefile.txt', 'utf8', function (err,data) {
        if (err) {
            return console.log("the error is: " + err);
        }
        console.log(data);
        myData = data;
        res.send(myData);
    });

I would suggest you should read more about Node.js and async method paradigm.

Thanks but I try to move the res.send(myData); inside as you did and i got the same error,any other idea ? — John Jerrby, Jun 05 '15 at 09:44

score 0 · Answer 3 · answered Jun 06 '15 at 07:07

Please post your error if you are getting any ?.Check the below answer.

var myData ;
    fs.readFile('C:\\Users\\jbt\\Desktop\\simplefile.txt', 'utf8', function (err,data) {
        if (err) {
            return console.log("the error is: " + err);
        }
        console.log(data);
        myData = data;
       res.end(myData);//If you are not using express
    });

I think it will help you.

Node error cannot set headers after they send

3 Answers3