Sending HTTP requests and receiving responses is an important feature of almost every application running in the browser. Most commonly, the technique used is termed Ajax. qooxdoo’s communication stack offers many ways to facilitate HTTP communication at different levels of abstraction.
At the very core, HTTP requests from the browser are made by interfacing with the HTTP client API or by adding a script tag to the document. Classes dealing with those low-level transport methods can be found in the qx.bom.request namespace. Usually they are not instantiated directly by the user.
Xhr is a wrapper of the HTTP client API offered by the browser. It’s purpose is to hide inconsistencies and to work around bugs found in popular implementations. The interface of qx.bom.request.Xhr is similar to XMLHttpRequest, the HTTP client API specified by the W3C.
Script is a script loader. Internally, the class deals with adding and removing script tags to the document and keeping track of the load status. Just like qx.bom.request.Xhr, the interface is modeled based on XMLHttpRequest.
Jsonp builds on the script loader and adds functionality needed to receive JSONP responses. JSONP stands for JSON with padding and is a technique to safely receive remote data. It's main advantage compared to to Xhr is that cross-origin requests are supported in all browsers.
Classes found in qx.io.request build on the groundwork laid by qx.bom.request. Properties allow to conveniently setup a request and fine-grained events facilitate handling changes of the request's status or response.
Note that historically, qooxdoo comes with two transport layers. The old transport layer is described below.
qx.io.rest.Resource is a client-side wrapper of a REST resource.