Express, Request Parameters

Request parameters

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

These are the main properties you’ll likely use:

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 using Content-Type: application/x-www-form-urlencoded, you will need to use the express.urlencoded() middleware:

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

app.use(express.urlencoded({
  extended: true
}))

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.