Creating an HTTP GET request to fetch JSON

One of the basic means of retrieving information from the server is using HTTP GET. This type of method in a RESTful manner should be only used for reading data. So, GET calls should never change server state. Now, this may not be true for every possible case, for example, if we have a view counter on a certain resource, is that a real change? Well, if we follow the definition literally then yes, this is a change, but it's far from significant to be taken into account.

Opening a web page in a browser does a GET request, but often we want to have a scripted way of retrieving data. This is usually to achieve Asynchronous JavaScript and XML (AJAX), allowing reloading of data without doing a complete page reload. Despite the name, the use of XML is not required, and these days, JSON is the format of choice.

A combination of JavaScript and the XMLHttpRequest object provides a method for exchanging data asynchronously, and in this recipe, we are going to...