Basic AJAX Request: XMLHttpRequest

By  on  

There are a number of common front-end tasks that many of us never touched the deep, dirty APIs for because our beloved JavaScript frameworks have provided easier ways to work with them.  That's why I wrote How JavaScript Event Delegation WorksDo a Basic HTTP Request with Node.js, and scores of tutorials about other low level API posts.  Next up is XMLHttpRequest, the API with which we use to make our AJAX calls!

Retrieving the XHR Object

Unlike most APIs, getting the core component is actually a bit of work since Internet Explorer used to require an ActiveX component to get AJAX to work:

var request;
if (window.XMLHttpRequest) { // Mozilla, Safari, ...
  request = new XMLHttpRequest();
} else if (window.ActiveXObject) { // IE
  try {
    request = new ActiveXObject('Msxml2.XMLHTTP');
  } 
  catch (e) {
    try {
      request = new ActiveXObject('Microsoft.XMLHTTP');
    } 
    catch (e) {}
  }
}

Bleh; the code is ugly but that's what you should expect behind the curtain, right?

Making a Request

Making a request requires two function calls:

request.open('GET', 'https://davidwalsh.name/ajax-endpoint', true);
request.send(null);

The open call defines the request type (get, post, etc.) and the send method executes the request.  Simple enough! Adding custom headers is simple too:

request.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded');

Request Callbacks

Of course making requests is somewhat useless if you don't handle the result, and there are two ways to set a callback:

// state changes
request.onreadystatechange = function() {
	if(request.readyState === 4) { // done
		if(request.status === 200) { // complete	
			console.log(request.responseText)
		}
	}
};

// addEventListener
function callbackFn(e) {
	// Handle each event
}
request.addEventListener("progress", callbackFn, false);
request.addEventListener("load", callbackFn, false);
request.addEventListener("error", callbackFn, false);
request.addEventListener("abort", callbackFn, false);

Choose whichever method you'd like but the addEventListener method is probably more elegant.

That's my simple introduction into creating simple AJAX requests with the native XMLHttpRequest API.  For further information about common AJAX tests, like sending form data, check out the Mozilla Developer Network!

Recent Features

  • By
    I’m an Impostor

    This is the hardest thing I've ever had to write, much less admit to myself.  I've written resignation letters from jobs I've loved, I've ended relationships, I've failed at a host of tasks, and let myself down in my life.  All of those feelings were very...

  • By
    How to Create a Twitter Card

    One of my favorite social APIs was the Open Graph API adopted by Facebook.  Adding just a few META tags to each page allowed links to my article to be styled and presented the way I wanted them to, giving me a bit of control...

Incredible Demos

  • By
    prefers-color-scheme: CSS Media Query

    One device and app feature I've come to appreciate is the ability to change between light and dark modes. If you've ever done late night coding or reading, you know how amazing a dark theme can be for preventing eye strain and the headaches that result.

  • By
    Telephone Link Protocol

    We've always been able to create links with protocols other than the usual HTTP, like mailto, skype, irc ,and more;  they're an excellent convenience to visitors.  With mobile phone browsers having become infinitely more usable, we can now extend that convenience to phone numbers: The tel...

Discussion

  1. On IE 7+ you don’t need the ActiveX object anymore. Just use the native XMLHttpRequest object. That would simplify your code sample a lot!

  2. Nice little article. I personally love jQuery’s handling of AJAX requests.

Wrap your code in <pre class="{language}"></pre> tags, link to a GitHub gist, JSFiddle fiddle, or CodePen pen to embed!