Supporting as many devices as possible, breaking RESTful APIs, etc.
A JS engine pre-supposes many, many things (too many) about a client, stuff like implicit assumptions that "this device has enough power and bandwidth to process my <insert length> javascript, perform appropriate security checks on it, handle this fast enough to service other requests in a timely manner, and also not take over the user's entire computer".
Accessibility means you should presume the least number of things possible. There's no sound, no visuals, no powerful cpu (maybe there isn't even a cpu), the device is the only working device from 20 years ago performing some critical function (e.g. government poverty assistance), there's only a couple minutes of power left, the internet is not available currently or quickly, etc.
You should never assume you have JS, period, and features should gracefully degrade in the presence of JS engines.
A JS engine pre-supposes many, many things (too many) about a client, stuff like implicit assumptions that "this device has enough power and bandwidth to process my <insert length> javascript, perform appropriate security checks on it, handle this fast enough to service other requests in a timely manner, and also not take over the user's entire computer".
Accessibility means you should presume the least number of things possible. There's no sound, no visuals, no powerful cpu (maybe there isn't even a cpu), the device is the only working device from 20 years ago performing some critical function (e.g. government poverty assistance), there's only a couple minutes of power left, the internet is not available currently or quickly, etc.
You should never assume you have JS, period, and features should gracefully degrade in the presence of JS engines.