Simple, easy-to-use, super-light, ajax() function wrapping XMLHttpRequest

ajax.js

/* 
Performs an AJAX (XMLHttpRequest) request where
    - method is the HTTP verb to use (e.g. 'POST')
    - dest is the destination endpoint path (e.g. '/api/endpoint')
    - type concerns how the response should be handled (e.g. 'json')
    - success is callback function that takes a response body
    - error is a callback funtion that takes a full error response object
    - data is data to send to the server (as in 'POST')
*/

function ajax(method, dest, type, success, error, data) {
    var req = new XMLHttpRequest();
    req.responseType = type;
    req.open(method, dest, true);
    req.onreadystatechange = function() {
        if (req.readyState == 4) {
            if (req.status == 200) {
                if (success) {
                    success(req.response);
                }
            } else {
                if (error) {
                    error(req);
                }
            }
        }
    }
    req.send(data);
}

/*
This ajax() function was adapted from code originally from stabping <https://github.com/icasdri/stabping>.
However it is released separately under the MIT license.

Copyright 2016 icasdri

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.
*/