Hash routing

Hash routing is a client-side technique used in single-page applications (SPAs) to manage navigation and state changes without reloading the entire page.

Early SPAs could not change the path part of the URL without reloading the page. To work around this, developers used hash-based SPA routing, which stores the route in the “fragment”, the part of the URL that follows the symbol #. Common patterns included #/profile and #!/profile. Applications continually checked window.location.hash (or listened for the hashchange event when it was supported later) to detect fragment changes during user navigation; the SPA then updated the view whenever the fragment changed.