Difference between app.use and app.get in express.js

I'm kind of new to express and node.js, and I can't figure out the difference between app.use and app.get. It seems like you can use both of them to send information. For example:

app.use('/',function(req, res,next) {
    res.send('Hello');
    next();
});

seems to be the same as this:

app.get('/', function (req,res) {
   res.send('Hello');
});

app.use() is intended for binding middleware to your application. The path is a "mount" or "prefix" path and limits the middleware to only apply to any paths requested that begin with it. It can even be used to embed another application:

// subapp.js
var express = require('express');
var app = modules.exports = express();
// ...

// server.js
var express = require('express');
var app = express();

app.use('/subapp', require('./subapp'));

// ...

By specifying / as a "mount" path, app.use() will respond to any path that starts with /, which are all of them and regardless of HTTP verb used:

  • GET /
  • PUT /foo
  • POST /foo/bar
  • etc.

app.get(), on the other hand, is part of Express' application routing and is intended for matching and handling a specific route when requested with the GET HTTP verb:

  • GET /

And, the equivalent routing for your example of app.use() would actually be:

app.all(/^\/.*/, function (req, res) {
    res.send('Hello');
});

app.use is the "lower level" method from Connect, the middleware framework that Express depends on.

Here's my guideline:

  • Use app.get if you want to expose a GET method.
  • Use app.use if you want to add some middleware (a handler for the HTTP request before it arrives to the routes you've set up in Express), or if you'd like to make your routes modular (for example, expose a set of routes from an npm module that other web applications could use).

app.get is called when the HTTP method is set to GET, whereas app.use is called regardless of the HTTP method, and therefore defines a layer which is on top of all the other RESTful types which the express packages gives you access to.