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 hostname as defined in the Host HTTP header value |
| .ip | the client 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-parsermodule to process POST data. This is no longer the case as of Express 4.16 (released in September 2017) and later versions.
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