Explain

How to get GET (query string) variables in Express.js on Node.js?

When building an Express.js application, you can access query string parameters (i.e., variables appended in the URL after the ? symbol) via req.query inside your route handlers. Below is a concise guide on how to do it.

1. Basic Usage

If you have a URL like:

GET /search?term=nodejs&page=2

You can read the query parameters in your route like this:

app.get('/search', (req, res) => {
  const term = req.query.term;  // "nodejs"
  const page = req.query.page;  // "2"

  // Do something with 'term' or 'page'
  res.send(`You searched for "${term}" on page ${page}`);
});

The req.query object automatically parses any key-value pairs in the query string and makes them accessible as properties.

2. Default / Fallback Values

If the URL doesn’t include certain query parameters, req.query will simply not have those properties. You can provide defaults or handle missing values:

app.get('/search', (req, res) => {
  const term = req.query.term || 'defaultTerm';
  const page = req.query.page || 1;
  // ...
});

3. Complex or Nested Query Parameters

By default, Express parses query parameters as simple key-value pairs. For example:

GET /users?role=admin&role=moderator

The result might be req.query.role = 'moderator', or 'admin' if you are using default Express query parsing without additional libraries.

If you need nested query structures or arrays, consider using a parsing library like qs, or configure Express to use a custom query parser. That said, for most use cases, the default req.query is enough.

4. Example With All Steps

const express = require('express');
const app = express();

app.get('/search', (req, res) => {
  // req.query is an object containing all query string parameters
  const { term, page } = req.query;

  // Provide defaults
  const searchTerm = term || 'nodejs';
  const currentPage = page || 1;

  res.json({
    searchTerm,
    currentPage
  });
});

app.listen(3000, () => {
  console.log('Server listening on port 3000');
});

Now, if you visit:

http://localhost:3000/search?term=express&page=2

You’ll receive a JSON response like:

{
  "searchTerm": "express",
  "currentPage": "2"
}

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Conclusion

To get GET (query) parameters in an Express.js application, reference req.query in your route handlers. This provides you an object containing all the key-value pairs from the URL query string. If you need more advanced parsing (e.g., nested objects), configure a custom query parser or use a library like qs.

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