For when I don't want to use jQuery or Angular to do a trivial POST HTTP request, neither do I care for raw XHR.

post.js

/*
* By Krish Dholakiya (itskrish.co, git.io/krish)
* MIT Licensed.
*
*     POST('http://example.com', {'keyOne': 'valueOne', 'keyTwo': 'valueTwo'}, function(response) {
*        var responseFromServer = response;
*     });
*
* TODO: use some sort of promise rather than callbacks
*/

window.POST = function (url, data, callback) {
     var xhr = new XMLHttpRequest();
     xhr.open('POST', url, true);
     var params = "";
     var loaded = false;
     var keys = Object.keys;
     keys(data).forEach(function(d) {
          if(params.length<1) {
               params = params + d + '=' + data[d];
          } else {
               params = params + '&' + d + '=' + data[d];
          }
     });
     xhr.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
     xhr.addEventListener('load', function(e) {
          if(callback) {
               callback(xhr.responseText);
          } else {
               return xhr.responseText;
          }
     }, false);
     xhr.send(params);
};