Express.JS regular expression for example.com/:username

Question

Express.JS regular expression for example.com/:username

// ex: http://example.com/john_smith
app.get('/^(a-z)_(0-9)', function(req, res) {
    res.send('user'); 
});

//  ex: http://example.com/john_smith/messages/1987234
app.get('/^(a-z)_(0-9)/messages/:id', function(req, res) {
    res.send('message');
});

I wrote the above code for an app that I want to pass a username as a url variable to node.js like I would do: $username = $_GET['username']; in PHP. I'm not too good at writing regular expressions so I wanted to see if anyone could set me on the right track. Thanks in advance.

regex
node.js
express

Answer 1

You're looking for req.params, which is an array of all of the capture groups in the regex.
The capture groups start at 1; req.params[0] is the entire match.

Answer 2

From your requirement it doesn't seem like you need a regular expression. Just use a a variable in your rule, like below:

// Grabs whatever comes after /user/ and maps it to req.params.id
app.get('/user/:id', function (req, res) {
    var userId = req.params.id;
    res.send(userId);
});

If you want to have better control, you could use a regular expression. To grab things you are interested in from the expression, use a capture group (which are typically expressed as a set of matching parenthesis):

// Grabs the lowercase string coming after /user/ and maps it to req.params[0]
app.get(/^\/user\/([a-z]+)$/, function (req, res) {
    var userId = req.params[0];
    res.send(userId);
});

A little off topic, but here's a really good intro to express.js that will help you understand it better (including how the routes work): http://evanhahn.com/understanding-express-js/