Node.js Tutorial - Node.js HTTP Headers

Setting Headers

You can explicitly queue any HTTP header in the response using the response.setHeader(name, value).

Content-Type in the response is the header we can set to inform how client would interpret the data from the server.

For example, if you are sending down an HTML file to the client, you should set the Content-Type to text/html, which you can with the following code:

response.setHeader("Content-Type", "text/html"); 

The formal name for the value of the Content-Type header is called MIME type.

MIME types for a few key content types are shown in the following Table.

NameMIME type
HyperText Markup Language (HTML)text/html
Cascading Style Sheets (CSS)text/css
JavaScript Object Notation (JSON)application/json
JPEG Imageimage/jpeg
Portable Network Graphics (PNG)image/png

There is a NPM package called mime (npm install mime), which you can use to get the official mime type from a file extension.

The following table shows how you can use it.

var mime = require('mime'); 
mime.lookup('/path/to/file.txt'); // => 'text/plain' 
mime.lookup('file.txt'); // => 'text/plain' 
mime.lookup('.TXT'); // => 'text/plain' 
mime.lookup('htm'); // => 'text/html' 

You can get a header that's queued for sending using the response.getHeader function:

var contentType = response.getHeader('content-type'); 

You can remove a header from the queue using the response.removeHeader function:


Send Headers Only

To explicitly send the headers and move the response into body only mode, call the response.writeHead member function.

response.writeHead member function takes the status code and optional headers that will be added to any headers queued using response.setHeader.

The following code shows how to set the status code to 200 and sets the Content-Type header for serving HTML:

response.writeHead(200, { 'Content-Type': 'text/html' }); 

Key Members of the Request Stream

The request is also a readable stream.

This is useful when the client wants to stream data to the server, for example, file upload.

The client HTTP request is split into a head and body part.

We can get useful information about the client request HTTP head.

The request.headers property is a JavaScript Object Literal of header names and values.


To check an individual header, index this object like any other JavaScript object literal:

console.log(request.headers['user-agent']); // 'curl/7.30.0'