Thursday, 27 November 2025

What JavaScript is Not Allowed to Do in the Browser

JavaScript in the browser is not normally allowed to do too much for security reasons.  

Stuff it cannot do includes anything OS related - specifically:

  • Cannot read/write arbitrary files
  • Cannot access hardware directly
  • Cannot control processes
JavaScript can do certain things through Web APIs:
  • DOM manipulation (HTML/CSS)
  • Local/session storage
  • IndexedDB (database built into the browser)
  • Cookies (with same origin)
  • Clipboard (with user permission)
  • Geolocation, camera, microphone (with user consent)

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