Summary  
Query parameters enable sending additional key-value data in the URL, accessible in Express via `req.query` for purposes like filtering, searching, or sorting data.

General domain of usage  
Building web APIs


Query parameters are used to send additional data in the URL.

They appear after a `?` and are written as key-value pairs.

Example:

* `'/users?active=true'`;
* `'/products?category=books'`.

In Express, query parameters are accessed using `req.query`.

```javascript id="u3k9rt"
app.get('/users', (req, res) => {
  const isActive = req.query.active;

  res.send(`Active: ${isActive}`);
});
```

If you open `'/users?active=true'`, the value of `isActive` will be `'true'`.

Query parameters are often used for filtering, searching, or sorting data.




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Query Parameters