There is HTML5 you can use now:
Compliant browsers will make it easier for users to specify numbers, by giving them a spinner. Other browsers just treat it as a text box. You need to validate the value server side anyway. Nothing breaks.
<input type="number" name="quantity">
New semantic tags such as header, footer, nav, article, section can be used depending on the level of support for old browsers with JS disabled you require. The page will work, the content will be visible, but if a user is on IE <=8 and has JS disabled you won't be able to style these elements. That's a steep minority.
In other cases there are polyfills that let you use native browser capabilities where they exist, and fill in the gaps with JS solutions where they don't. If a site is built with progressive enhancement this won't lead to anyone missing out on content.