Raw JS AJAX method

Question

I built this as a simple example of using raw JS to perform a simple GET request with a data callback.

Suggestions on how this could be improved in any way, while keeping it simple, would be much appreciated.

JS:

/*jslint unparam: true, white: true */
var app = (function() {
 "use strict";
 return {
 ajax: function(url, callback) {
 var xmlhttp = new window.XMLHttpRequest();
 xmlhttp.onreadystatechange = function() {
 var data;
 if (xmlhttp.readyState === 4 && xmlhttp.status === 200) {
 data = xmlhttp.responseText;
 if(typeof callback === 'function') {
 callback(data);
 }
 }
 };
 xmlhttp.open('GET', url, true);
 xmlhttp.send();
 }
 };
}());

Example usage:

app.ajax('file.json', function(data) {
 data = JSON.parse(data);
 console.log(data.name);
});

• Vogel612: you are aware this is not cross-browser compatible? here's something I used when I did something similar
• Alex Garrett: @Vogel612 Do you mean with regards to IE6/7?
• Vogel612: yea. Don't expect ppl. on public websites to have current browsers. no offense if you don't implement it though ;) It's just a hassle for that minimal helpfulnes.
• Alex Garrett: I don't really care that much about IE6/7 support. Thanks for pointing this out anyway.
• konijn: I rolled back your edit, it is considered bad form to update this question because it puts answer <> question out of sync.

Answer 1

From a once over:

• There should be a way to handle errors, this is only good for sunny day scenarios
• It would be more useful if you also passed the xmlhttp object to the callback : callback(data, xmlhttp);
• As stated by Vogel612, it wont work for some versions of IE, it's not hard to add support for those
• There is no need at all to declare data, you can pass xmlhttp.responseText; straight to callback, it would make the code tighter
• A comment as to what 4 and 200 stand for could be useful for the unaware reader

Other than that, looks good.

• Marc-Andre: Here at Code Review we don't like magic numbers +1 !
• Alex Garrett: Thanks for the feedback. I've updated the solution in the original question.