Route Parameters in Express
Route Parameters in Express
In Express, route parameters are essentially
variables derived from named sections of the URL. Express captures
the value in the named section and stores it in the req.params property.
const
app = require
('express'
)();
app.get('/user/:userId'
, (req, res) => {
req.params;
res.json(req.params);
});
const
server = await
app.listen(3000
);
const
axios = require
('axios'
);
const
res = await
axios.get('http://localhost:3000/user/42'
);
res.data; You can define multiple route parameters in a URL. In the below example,
the Express route is /users/:userId/books/:bookId, so req.params.userId
will contain the substring after /users/ and before /books/, and req.params.bookId will contain everything after /books/.
const
app = require
('express'
)();
app.get('/user/:userId/books/:bookId'
, (req, res) => {
req.params;
res.json(req.params);
});
const
server = await
app.listen(3000
);
const
axios = require
('axios'
);
const
res = await
axios.get('http://localhost:3000/user/42/books/101'
)
res.data; Why Route Parameters?
Route parameters have some convenient properties that reduce the amount of
validation you need to do versus using query parameters or request bodies:
- A route parameter is never
nullorundefined. For example, a request toGET /usersabove will cause an HTTP 404, and not call the route handler for/users/:userId/books/:bookId. - A route parameter is always a string with positive length. For example,
GET /user/42/books/also causes an HTTP 404.
If you’re defining an HTTP API in Express, it is usually better to make a
parameter a route parameter rather than a query parameter or a body parameter
if possible. If your parameter is mandatory and doesn’t need to be an object,
route parameters are generally the way to go.
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