In a lot of cases you shouldn't even use Javascript for this, responsive layouts can be built using CSS media queries based on viewport size. More advanced web

In a lot of cases you shouldn't even use Javascript for this, responsive layouts can be built using CSS media queries based on viewport size. More advanced webapps might occasionally need to do something fancier than that if the mobile vs desktop functionality is (for some reason) substantially different instead of just rearranged. https://developer.mozilla.org/en-US/docs/Web/CSS/Media_Queries/Using_media_queries https://developer.mozilla.org/en-US/docs/Web/CSS/Media_Queri...