The Same Origin Policy (SOP) is a security measure standardized among browsers. It is needed to prevent Cross-Site Request Forgery (CSRF). The "Origin" mostly refers to a "Domain". Same Origin Policy prevents different origins (domains) from interacting with each other, to prevent attacks such as CSRF (Cross Site Request Forgery) through such requests, like AJAX. In other words, the browser would not allow any site to make a request to any other site. Without Same Origin Policy , any web page would be able to access the DOM of other pages.
If you need to enable CORS on the server in case of localhost, you need to have the following on request header.