Why do browsers allow cross-domain JavaScript to execute but not XMLHttpRequests?
7th December 2010
My answer to Why do browsers allow cross-domain JavaScript to execute but not XMLHttpRequests? on Quora
It’s called the Same Origin Policy, and it’s principally about intranets. Imagine you have a URL http://intranet.corp/top-secret-...—and you then visit http://evil.example.com/ . If cross domain XHR was allowed the evil site could suck that secret document off your intranet without you realising.
JavaScript should really have the same restrictions (I shouldn’t be able to load http://intranet.corp/top-secret-... ) but as I understand it no one spotted the problem until the entire Internet economy was already dependent on externally hosted scripts as a business model.
More recent articles
- The new GPT-5.6 family: Luna, Terra, Sol - 9th July 2026
- sqlite-utils 4.0, now with database schema migrations - 7th July 2026
- sqlite-utils 4.0rc2, mostly written by Claude Fable (for about $149.25) - 5th July 2026