What is CORS?

When it comes to HTTP, an origin is defined by several different aspects of a URL. As mentioned in a previous article, the origin is composed of the following:

• The protocol (e.g. http or https)
• The hostname (e.g. 30secondsofcode.org)
• The port (e.g. 80 or 3000)

As long as all three of these match, the browser considers the two URLs to be same-origin. If any of these aspects differ, the browser considers the two URLs to be cross-origin. It might be helpful to look at some examples of different origins to clarify:

• The hostname (e.g. 30secondsofcode.org)
• The port (e.g. 80 or 3000)

As long as all three of these match, the browser considers the two URLs to be same-origin. If any of these aspects differ, the browser considers the two URLs to be cross-origin. It might be helpful to look at some examples of different origins to clarify:

• http://30secondsofcode.org and https://www.30secondsofcode.org (different protocols)
• http://www.30secondsofcode.org and http://dev.30secondsofcode.org (different hostnames)
• https://30secondsofcode.org and https://30secondsofcode.org:3000 (different ports)

From 30-seconds-of-code: cors-explained