Express Object

Creates an Express application. The express() function is a top-level function exported by the express module.

const express = require('express');
const app = express();

Methods

The Express object has the following methods that can be used to create middleware functions, routers and have some built-in middleware:

express.json([options])

This is a built-in middleware function in Express. It parses incoming requests with JSON payloads and is based on body-parser.

Returns middleware that only parses JSON and only looks at requests where the Content-Type header matches the type option. This parser accepts any Unicode encoding of the body and supports automatic inflation of gzip and deflate encodings.

A new body object containing the parsed data is populated on the request object after the middleware (i.e. req.body), or undefined if there was no body to parse, the Content-Type was not matched, or an error occurred.

The following table describes the properties of the optional options object.

express.raw([options])

This is a built-in middleware function in Express. It parses incoming request payloads into a Buffer and is based on body-parser.

Returns middleware that parses all bodies as a Buffer and only looks at requests where the Content-Type header matches the type option. This parser accepts any Unicode encoding of the body and supports automatic inflation of gzip and deflate encodings.

A new body Buffer containing the parsed data is populated on the request object after the middleware (i.e. req.body), or undefined if there was no body to parse, the Content-Type was not matched, or an error occurred.

The following table describes the properties of the optional options object.

express.Router([options])

Creates a new router object.

const router = express.Router([options]);

The optional options parameter specifies the behavior of the router.

You can add middleware and HTTP method routes (such as get, put, post, and so on) to router just like an application.

For more information, see Router.

express.static(root, [options])

This is a built-in middleware function in Express. It serves static files and is based on serve-static.

The root argument specifies the root directory from which to serve static assets. The function determines the file to serve by combining req.url with the provided root directory. When a file is not found, instead of sending a 404 response, it instead calls next() to move on to the next middleware, allowing for stacking and fall-backs.

The following table describes the properties of the options object. See also the example below.

For more information, see Serving static files in Express. and Using middleware - Built-in middleware.

dotfiles

Possible values for this option are:

• “allow” - No special treatment for dotfiles.
• “deny” - Deny a request for a dotfile, respond with 403, then call next().
• “ignore” - Act as if the dotfile does not exist, respond with 404, then call next().

fallthrough

When this option is true, client errors such as a bad request or a request to a non-existent file will cause this middleware to simply call next() to invoke the next middleware in the stack. When false, these errors (even 404s), will invoke next(err).

Set this option to true so you can map multiple physical directories to the same web address or for routes to fill in non-existent files.

Use false if you have mounted this middleware at a path designed to be strictly a single file system directory, which allows for short-circuiting 404s for less overhead. This middleware will also reply to all methods.

setHeaders

For this option, specify a function to set custom response headers. Alterations to the headers must occur synchronously.

The signature of the function is:

fn(res, path, stat);

Arguments:

• res, the response object.
• path, the file path that is being sent.
• stat, the stat object of the file that is being sent.

Example of express.static

Here is an example of using the express.static middleware function with an elaborate options object:

const options = {
  dotfiles: 'ignore',
  etag: false,
  extensions: ['htm', 'html'],
  index: false,
  maxAge: '1d',
  redirect: false,
  setHeaders(res, path, stat) {
    res.set('x-timestamp', Date.now());
  },
};

app.use(express.static('public', options));

express.text([options])

This is a built-in middleware function in Express. It parses incoming request payloads into a string and is based on body-parser.

Returns middleware that parses all bodies as a string and only looks at requests where the Content-Type header matches the type option. This parser accepts any Unicode encoding of the body and supports automatic inflation of gzip and deflate encodings.

A new body string containing the parsed data is populated on the request object after the middleware (i.e. req.body), or undefined if there was no body to parse, the Content-Type was not matched, or an error occurred.

The following table describes the properties of the optional options object.

express.urlencoded([options])

This is a built-in middleware function in Express. It parses incoming requests with urlencoded payloads and is based on body-parser.

Returns middleware that only parses urlencoded bodies and only looks at requests where the Content-Type header matches the type option. This parser accepts only UTF-8 encoding of the body and supports automatic inflation of gzip and deflate encodings.

A new body object containing the parsed data is populated on the request object after the middleware (i.e. req.body), or undefined if there was no body to parse, the Content-Type was not matched, or an error occurred. This object will contain key-value pairs, where the value can be a string or array (when extended is false), or any type (when extended is true).

The following table describes the properties of the optional options object.