Retrieve the GET query string parameters using Express

The query string is the part that comes after the URL path, and starts with a question mark ?. Express exposes it through req.query, regardless of the HTTP method. Data sent in a request body uses req.body instead.

For example:

?name=flavio

Multiple query parameters can be added using &:

?name=flavio&age=35

How do you get those query string values in Express?

Express makes it very easy by populating the Request.query object for us:

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

app.get('/', (req, res) => {
  console.log(req.query)
})

app.listen(8080)

This object is filled with a property for each query parameter.

If there are no query params, it’s an empty object.

This makes it easy to iterate on it using the for…in loop:

for (const key in req.query) {
  console.log(key, req.query[key])
}

This will print the query property key and the value.

You can access single properties as well:

req.query.name //flavio
req.query.age //35

Repeated keys like ?tag=js&tag=node give you an array: req.query.tag is ['js', 'node'].

Nested query parameters in Express 5

Express 5 uses the “simple” query parser by default. Flat parameters like the ones above work exactly the same, but brackets don’t create nested objects anymore.

With ?user[name]=flavio&user[age]=35 you get this:

{ 'user[name]': 'flavio', 'user[age]': '35' }

If you want the nested object { user: { name: 'flavio', age: '35' } }, which is what Express 4 gave you, switch to the extended parser when you create the app:

const app = express()
app.set('query parser', 'extended')

One more change: req.query is read-only in Express 5. Assigning a new value to it does nothing (or throws in strict mode), so if you need to tweak the values, copy them first with const query = { ...req.query }.

The query string is only one of the things you can read from the request. Here’s a reference of all the request properties, and if your data comes from a form instead, see how to read POST parameters.

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