You can clone with
HTTPS or Subversion.
async as less support than defer, but async takes priority over defer.
Might also be worthwhile mentioning the implications if multiple scripts have these attributes; the order of script execution cannot reliably be determined when using async.
defer DOES NOT WORK unless your site completely doesnt care about IE9.
Thanks @paulirish – what a shame. Took a while to get through the issue you referred to, but it was worth it.
Would the blanket of "don't use" flag still stand for a synchronous Modernizr script in the head and a defer script in the footer that depended on it?
Additionally, would there be any benefit to a site using a single defer script which used some sort of require.js process for other scripts within?
Thanks for cc-ing me on this, Adam. I was unaware of the defer bugs described in that thread. It sounds like it's safe to use defer with scripts that don't perform DOM manipulation, though.
Cheers for the answers Paul. If I come across this somewhere else I'll try update and link them through to the h5bp issue.