How to set custom favicon in Express?

No need for custom middleware?! In express:

 //you probably have something like this already    
app.use("/public", express.static('public'));

Then put your favicon in public and add the following line in your html's head:

<link rel="icon" href="/public/favicon.ico">

In Express 4

Install the favicon middleware and then do:

var favicon = require('serve-favicon');

app.use(favicon(__dirname + '/public/images/favicon.ico'));

Or better, using the path module:

app.use(favicon(path.join(__dirname,'public','images','favicon.ico')));

(note that this solution will work in express 3 apps as well)

According to the API, .favicon accepts a location parameter:

app.use(express.favicon("public/images/favicon.ico"));

Most of the time, you might want this (as vsync suggested):

app.use(express.favicon(__dirname + '/public/images/favicon.ico'));

Or better yet, use the path module (as Druska suggested):

app.use(express.favicon(path.join(__dirname, 'public','images','favicon.ico')));

According to the package description:

This module caches the icon in memory to improve performance by skipping disk access.
This module provides an ETag based on the contents of the icon, rather than file system properties.
This module will serve with the most compatible Content-Type.

No extra middlewares required. Just use:

app.use('/favicon.ico', express.static('images/favicon.ico'));