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.


/*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') {

            xmlhttp.open('GET', url, true);


Example usage:

app.ajax('file.json', function(data) {
    data = JSON.parse(data);
  • \$\begingroup\$ you are aware this is not cross-browser compatible? here's something I used when I did something similar \$\endgroup\$
    – Vogel612
    Commented Mar 19, 2014 at 12:08
  • \$\begingroup\$ @Vogel612 Do you mean with regards to IE6/7? \$\endgroup\$ Commented Mar 19, 2014 at 12:14
  • \$\begingroup\$ 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. \$\endgroup\$
    – Vogel612
    Commented Mar 19, 2014 at 12:15
  • 1
    \$\begingroup\$ I don't really care that much about IE6/7 support. Thanks for pointing this out anyway. \$\endgroup\$ Commented Mar 19, 2014 at 12:24
  • \$\begingroup\$ I rolled back your edit, it is considered bad form to update this question because it puts answer <> question out of sync. \$\endgroup\$
    – konijn
    Commented Mar 19, 2014 at 13:41

1 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.

  • \$\begingroup\$ Here at Code Review we don't like magic numbers +1 ! \$\endgroup\$
    – Marc-Andre
    Commented Mar 19, 2014 at 13:04
  • \$\begingroup\$ Thanks for the feedback. I've updated the solution in the original question. \$\endgroup\$ Commented Mar 19, 2014 at 13:39

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