Request parameters

I mentioned how the Request object holds all the HTTP request information.

These are the main properties you’ll likely use:

Property Description
.app holds a reference to the Express app object
.baseUrl the base path on which the app responds
.body contains the data submitted in the request body (must be parsed and populated manually before you can access it)
.cookies contains the cookies sent by the request (needs the cookie-parser middleware)
.hostname the server hostname
.ip the server IP
.method the HTTP method used
.params the route named parameters
.path the URL path
.protocol the request protocol
.query an object containing all the query strings used in the request
.secure true if the request is secure (uses HTTPS)
.signedCookies contains the signed cookies sent by the request (needs the cookie-parser middleware)
.xhr true if the request is an XMLHttpRequest

How to 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 ?.

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

How to retrieve the POST query string parameters using Express

POST query parameters are sent by HTTP clients for example by forms, or when performing a POST request sending data.

How can you access this data?

If the data was sent as JSON, using Content-Type: application/json, you will use the express.json() middleware:

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

app.use(express.json())

If the data was sent as JSON, using Content-Type: application/x-www-form-urlencoded, you will use the express.urlencoded() middleware:

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

app.use(express.urlencoded())

In both cases you can access the data by referencing it from Request.body:

app.post('/form', (req, res) => {
  const name = req.body.name
})

Note: older Express versions required the use of the body-parser module to process POST data. This is no longer the case as of Express 4.16 (released in September 2017) and later versions.