Cross-origin resource sharing
Where applicable the Path of Exile API implements cross-origin resource sharing to allow cross domain access. In general this means that you can do a cross domain request with no extra work. Note that this will only work with modern browsers. Alternatively you may use JSON-P callbacks.
JSON-P callbacks
JSON-P is another method to access data cross domain. API GET methods support a callback
argument which wraps the resulting JSON in a function call to the function name you provide.
If you are using a library such as jQuery methods such as jQuery.ajax support this out of the box by setting the dataType to "jsonp".
$.ajax({ url: 'https://api.pathofexile.com/league/Hardcore', dataType: 'jsonp' }).done(function(league) { console.log("Got", league.id, "league"); });
Note that there are a few basic restrictions in place on the allowed characters for the callback. More information on JSON-P can be found here.