The normal XMLHttpRequest object is not very useful in SlimerJS because the script is executing from the origin of “about:blank”. The same-origin policy prevents XMLHttpRequest from being used with most servers.
To avoid this, we can use the Add-ons SDK version of XMLHttpRequest which is bundled with SlimerJS, as follows:
var XMLHttpRequest = require('sdk/net/xhr').XMLHttpRequest;
This version of XMLHttpRequest is unrestricted; you should avoid using it on untrusted input as it can fetch anything including local files.
Note that requests made with this XMLHttpRequest won’t call any network callbacks, but AJAX requests from within loaded web pages will do so.