Chapter 1. The Core of CORS

This chapter covers

  • Which issues CORS solves
  • How a CORS request works
  • The benefits of CORS

Suppose you’re building a web mashup to load photos from the New York Public Library’s (NYPL) Flickr page and display them on your own page. What would the code look like? You could start with an HTML page to display the photos, add JavaScript code to load the photos from the Flickr page, and display them on the page. Pretty straightforward, right?

But if you were to run this code in the browser, it wouldn’t work because the browser’s same-origin policy limits client code from making HTTP requests to different origins. This means that a web page running from your desktop or web server can’t make an HTTP request to Flickr.com. ...

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