Part 1. Introducing CORS

Cross-Origin Resource Sharing (CORS) enables web clients to make HTTP requests to servers hosted on different origins. CORS is a unique web technology in that it has both a server-side and a client-side component. The server-side component configures which types of cross-origin requests are allowed, while the client-side component controls how cross-origin requests are made.

Part 1 focuses on the client-side component of CORS. Chapter 1 is an introduction to CORS, how it works, and its benefits. It also gives a taste of what CORS looks like by introducing a sample application that makes CORS requests to the Flickr API.

Chapter 2 dives deeper into this sample application to show how the client-side component of CORS works. It starts by looking at how the browser’s XMLHttpRequest object (which is already familiar to any developer making same-origin requests) can be used to make cross-origin requests. Then, it turns to Internet Explorer 8 and Internet Explorer 9, which support a subset of CORS via the XDomainRequest object. Next, it looks at other places where CORS requests turn up, such as the canvas element. The chapter concludes by looking at how CORS requests can be made from jQuery.