Error [Err_Http_Headers_Sent] – Cannot Set Headers After They Are Sent To The Client

If you see the Node.js HTTP error, ERR_HTTP_HEADERS_SENT, there’s likely a problem with the reaction within your code. Your web server may be trying a number of times to get to a client as well as failing because it can’t discover the header.

The solution for this tends to be fairly simple. Throughout this article, we’ll review where this mistake stays in the Node.js hierarchy, what it is, and also how to repair it.

The Node.js HTTP Technical Rundown

The ERR_HTTP_HEADERS_SENT is a runtime mistake that lies with the Node.js Error.code pecking order:



The nice feature of errors within the “Error.code” is that their names normally reflect what kind of error you are obtaining. So, in this instance, the error will certainly have something to do with HTTP headers.

What is the ERR_HTTP_HEADERS_SENT Error?

According to the Node.js docs, an ERR_HTTP_HEADERS_SENT is “an effort made to add more headers after the headers [have] currently been sent out.”

Allow’s damage this down a little bit.

If you’re getting this error, this suggests that a part of your code is trying to send a header after the body has actually currently been written to the HTTP reaction. It resembles when you send a formal letter. The letter can only be sent out if you consist of an address. Without an address, your letter isn’t going anywhere, which suggests that nobody will certainly have the ability to read its content. The headers and also body on an HTTP receptive work the same way. When sending out headers with your HTTP action, you have to compose the headers prior to sending the body, otherwise you won’t have the ability to send out the content of the body.

Since you recognize a little bit about this specific error, it’s time to discover exactly how to fix it.

How to Take care of an ERR_HTTP_HEADERS_SENT

As developers, you have options regarding exactly how you intend to code. You might code making use of just Node.js, or you might be using the Express.js structure. Due to the fact that both stand ways to code making use of Node.js, we’ll look at this mistake for both Node.js as well as Express.js.

Node.js Instance

Right here’s an instance of what your code might resemble if you’re just utilizing Node.js:

const http = call for(‘ http’);.

web server = http.createServer( feature (req, res) plain’);.


). pay attention( 8080 );.

As well as, as soon as you run it and issue this request: crinkle -i localhost:8080, the server will die with this output:.

_ http_outgoing. js:561.

throw brand-new ERR_HTTP_HEADERS_SENT(‘ established’);.


Error [ERR_HTTP_HEADERS_SENT]: Can not set headers after they are sent to the customer.

at ServerResponse.setHeader (_ http_outgoing. js:561:11).

at Server.<anonymous> (/ Users/ssb/src/ node-tmp/server. js:5:7).

at Server.emit (events.js:376:20).

at parserOnIncoming (_ http_server. js:896:12).

at HTTPParser.parserOnHeadersComplete (_ http_common. js:126:17)


Yikes! So, what did we do wrong right here?

As we reviewed in the past, an HTTP response to a customer has to have its headers created before the body of the reaction.

res.write(‘ Hello there, Globe!’);.

res.setHeader(‘ X-Foo’, ‘bar’);.

res.setHeader(‘ Content-Type’, ‘text/plain’);.

The res.setHeader is called after the res.write, unavoidably causing an ERR_HTTP_HEADERS_SENT error.

Below’s what the code ought to resemble.

res.setHeader(‘ X-Foo’, ‘bar’);.

res.setHeader(‘ Content-Type’, ‘text/plain’);.

res.write(‘ Hello there, Globe!’);.

If you’re receiving this error, take a minute and inspect your code. Try to find instances where the body procedes the header.

Express.js Example.

As a programmer collaborating with Node.js code, you could be using the Express.js framework. Code that creates the ERR_HTTP_HEADERS_SENT mistake will certainly look a bit various contrasted to Node.js code.

Below’s an instance of Express.js code that will certainly generate this error:.

const express = call for(‘ express’).

const application = share().

const port = 8080.

app.get(‘/’, (req, res) =&

res.send(‘ Hey there Globe!’).

res.setHeader(‘ X-Foo’, ‘bar’).


app.listen( port, () =& ).

Once you run the HTTP server and crinkle the endpoint with curl -i localhost:8080, your terminal will certainly spit out the following error:.

Error [ERR_HTTP_HEADERS_SENT]: Can not set headers after they are sent to the client.

at ServerResponse.setHeader (_ http_outgoing. js:561:11).

at/ Users/ssb/src/ node-tmp/index. js:7:7.

The code over generates this mistake as a result of this block:.

app.get(‘/’, (req, res) =&

res.send(‘ Hey there Globe!’).

res.setHeader(‘ X-Foo’, ‘bar’).


The body of the code is sent before the header. As you know, you can not send out the body prior to the header. Repair this by revising your code the adhering to means:.

app.get(‘/’, (req, res) =&

res.setHeader(‘ X-Foo’, ‘bar’).

res.send(‘ Hi Globe!’).


Which’s it! It’s a basic repair for a frustrating error.

Exactly how Do I Discover This Node.js HTTP Error?

Without an error tracking software application or debugger, the only way to discover this mistake is to go through your logs. With hundreds, otherwise thousands, of lines of code to sort through, this can show to be a lengthy endeavor simply to locate one mistake. That’s where Airbrake Error as well as Efficiency Monitoring can be found in. With Airbrake Node.js and also Express.js Error Monitoring, you can skip the logs and also go straight to the code that’s generating the ERR_HTTP_HEADERS_SENT mistake.</anonymous>