@Rawrplus the madia thingy applies certain rules on certain elements in certain sizes.
Meaning that if the size (width) of the screen is lower than X, than there will be a different style/formatting for elements declared within @media , with no option to switch it back to desktop view.
What if there is someone who likes the desktop website, someone that is not on 3G and doesnt care about mobile data, someone who is using super fast wifi (a decent one

) and cba to wait 1-2 seconds more. He would definitely want to switch to desktop. Thats where the JS comes in handy.