Express Type

The express type response object method can be used to quickly set the Content-Type response header to a desired mime type, and in most cases it will work fine, but it might still be better to use the res.set method as a way to set Content-Type to make sure that the correct mime type is set for the content that is being sent to the browser. Never the less this will be a quick post on the express type convenience method as well as some related topics with Content-Type and response headers.

1 - Express Type basic example

So the express type response method can be used to quickly set the Content Type response header using just a simple string that represents a typical file extension , or simple typical name. For example if I want some html that is being sent to render as plain text I can just pass the string ‘text’, ‘txt’, or ‘.txt’ to the res.type method.

let express = require('express'),
app = express();
 
app.get('/', (req, res) => {
    res.type('text');
    console.log(res.get('Content-Type')); // 'text/plain; charset=utf-8'
    res.send('<h1>This should just be plain text so the tags should show in the browser</h1>')
});
 
app.listen(8080);

1.1 - Express Response Set method can also be used to to do the same thing

The above example of the Express Type method can also be used with the response set method as well. One way or another what needs to happen is to just simply set the Content-Type response header. The Express type response method is just a convenience method to set just the Content-Type header, but only that header. The Response set method can be used to set that header as well as any other header, the only draw back is that you need to know your mime types, and be sure that you are setting the right one.

let express = require('express'),
app = express();
 
app.get('/', (req, res) => {
    res.set('Content-Type','text/plain');
    console.log(res.get('Content-Type')); // 'text/plain; charset=utf-8'
    res.send('<h1>Some Html again</h1>')

});
 
app.listen(8080);

It generally might be better to use the response set method in replace of the type method, it gives a greater deal of control of mime types, and in addition I can use it to set multiple headers at once as well. I will write more about the response set method as a way to set Content-Type in express in a later section in this post.

2 - Express Type and express static

When using express static as a way to serve static assets such as javaScript files it is impotent to set the proper mime type for assets like javaScript files. When using the espress type response method the mime type set for javaScipt files is application/javascript, which is one the list at iana.org, however in mozilla documentation it is recommended to use text/javaScript.

let express = require('express'),
app = express();
 
app.use('/js', express.static('public/js', {
        extensions: ['.js'],
        index: false,
        setHeaders: (res, path, stat) => {
            res.type('js');
            console.log(res.get('Content-Type'));
            // application/javascript; charset=utf-8
        }
    }));
 
app.use('/', express.static('public/html', {
        extensions: ['.html'],
        setHeaders: (res, path, stat) => {
            res.type('html');
            console.log(res.get('Content-Type'));
            // text/html; charset=utf-8
        }
    }));
 
app.listen(8080);

In most cases the mime type that is set by the type method will work just fine, but this is one thing that comes to mind as to why it might be better to just use the set response method instead, and just know what headers, and values are important and why. Sometimes it might be necessary to just set the Content-Type header manually, but using the set request method I always have a clear understanding of what I am setting for mime type..

3 - Response Set method as an alternative to The Express Type response method

Another nice thing about using the set response method as a way to set the Content-Type header, is that I can set more than one header by giving an object of header field names for each key, and of source the field value for each corresponding object key value.

So If I want to set the Content-Type, and another header such as Cache-Control I can do so with just a single call with the set method, rather than using the type method to just set the Content-Type header, and then the set method to set Cache-Control.

let express = require('express'),
app = express();
 
let n = 0;
app.get('/', (req, res) => {
    res.set({
        'Content-Type': n === 0 ? 'text/plain' : 'text/html',
        'Cache-Control': 'no-store'
    });
    console.log(res.get('Content-Type'));
    res.send('<h1>just some html</h1>');
    n += 1;
    n %= 2;

});
 
app.listen(8080);