How to use XmlHttpRequests to Send POST to Server

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So, you need to send some bits of information from your browser to the server in order to complete some processing. Maybe you need the information to search for something in a database, or just to update something on your server. Today I am going to show you how to send some data to your server from the client through a POST request using XmlHttpRequest. First, we need to set up our environment!

Set up

The first thing to make sure you have is Node and NPM installed.

Create a new directory for your project; here we will call it xhr-post:

$ mkdir xhr-post
$ cd xhr-post

Then we would like to install express.js and body-parser:


$ npm install express
$ npm install body-parser

Express makes it easy for us to handle HTTP requests, and body-parser allows us to parse incoming request bodies. Let’s create two files: one for our server called server.js and one for our front end code called index.html. Then initialize your repo with a package.json file by doing:

$ npm init

Client

Now it’s time to start with some front end work. Open and edit your index.html file with:

<!doctype html>
<html>
   <h1>
   XHR POST to Server
   </h1>
   <body>
     <input type='text' id='num' />
     <script>
       function send () {
         var number = {
           value: document.getElementById('num').value
         }
         var xhr = new window.XMLHttpRequest()
         xhr.open('POST', '/num', true)
         xhr.setRequestHeader('Content-Type', 'application/json;charset=UTF-8')
         xhr.send(JSON.stringify(number))
       }
     </script>
     <button type='button' value='Send' name='Send' onclick='send()' >
       Send
     </button>
   </body>
</html>

This file simply has a input field to allow users to enter some information, and a button to then send the information entered to the server. What we should focus on here is the button’s onclick method send().

This is the function that is called once the button is clicked. We create a JSON object to hold the value from the text field. Then we create a new instance of an XMLHttpRequest with xhr. We call xhr.open() to initialize our request by giving it a request method (POST), the url we would like to open the request with (‘/num’) and determine if it should be asynchronous or not (set true for asynchronous).

We then call xhr.setRequestHeader(). This sets the value of the HTTP request to json and UTF-8.

As a last step, we send the request with xhr.send(). We pass the value of the text box and stringify it to send the data as raw text to our server, where it can be manipulated.

Server

Here our server is supposed to handle the POST request and we are simply going to log the request received from the client.

const express = require('express')
const app = express()
const path = require('path')
var bodyParser = require('body-parser')
var port = 3000

app.listen(port, function () {
console.log('We are listening on port ' + port)
})

app.use(bodyParser.urlencoded({extended: false}))
app.use(bodyParser.json())

app.get('*', function (req, res) {
res.sendFile(path.join(__dirname, '/index.html'))
})

app.post('/num', function (req, res) {
var num = req.body.value
console.log(num)
return res.end('done')
})

At the top, we declare our variables, obtaining an instance of express, path and body-parser. Then we set our server to listen on port 3000.

Next, we use bodyParser object to decide what kind of information we would like to parse, we set it to json because we sent a json object from our client, if you recall the last section. This is done with:

app.use(bodyParser.json())

Then we serve our html file in order to see our front end created in the last section with:

app.get('*', function (req, res) {
res.sendFile(path.join(__dirname, '/index.html'))
})

The last part of server.js is where we handle the POST request from the client. We access the value sent over by checking for corresponding property on the body object which is part of the request object. Then, as a last step for us to verify we have the correct information, we will log the data received to the console and send a response to the client.

Test

Let’s test what we have done. In the project directory, we can run:

$ node server.js

Open your web browser and go to the url localhost:3000. This is what your web page should look like:

This is what your output to the console should look like if you enter a 5 in the input field:

Conclusion

You are all done! You now have a web page that sends some JSON data to your server using XmlHttpRequest! Here is a summary of what we went over:

  1. Created a front end with an input field and button
  2. Created a function for our button to send an XmlHttpRequest
  3. Created our server to listen on port 3000
  4. Served our html file
  5. Handled our POST request at route ‘/num’
  6. Logged the value to our console

If you enjoyed this post, share it on twitter. Check out the code for this tutorial on GitHub.

Possible Resources

Check out my GitHub

View my personal blog

Information on XmlHtttpRequest

GitHub pages for:

express

body-parser

About the author

Antonio Cucciniello is a software engineer with a background in C, C++, and JavaScript (Node.Js). He is from New Jersey, USA. His most recent project called Edit Docs is an Amazon Echo skill that allows users to edit Google Drive files using their voice. He loves building cool things with software, reading books on self-help and improvement, finance, and entrepreneurship. To contact Antonio, e-mail him at [email protected], follow him on twitter at @antocucciniello, and follow him on GitHub here: https://github.com/acucciniello.

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