AFAIK the scripts cannot be parsed and executed in parallel since they're not explicitly async. The browser doesn't know if any of the following scripts may depend on the previous ones (think jQuery), so it just downloads them and then waits to parse and execute them in order, blocking rendering.
It's true that delivering them in parallel may in some cases reduce the actual download time, but given the small file sizes Apple is serving, the connection overhead (TCP handshake, HTTP headers, slow start, ...) just makes it worse. Most browsers (especially mobile ones) aren't even going to download more than 4-6 files at a time, since they're not using domain sharding.
>It's true that delivering them in parallel may in some cases reduce the actual download time, but given the small file sizes Apple is serving, the connection overhead (TCP handshake, HTTP headers, slow start, ...) just makes it worse. Most browsers (especially mobile ones) aren't even going to download more than 4-6 files at a time, since they're not using domain sharding.
So what I'm wondering is if you target that 4-6 connection limit, if you get all your js files to load in one connection group can you benefit from the parallel downloading while not blocking anything? Like this: http://i.imgur.com/iuriZ.png
Seems to me like the handshake issue goes away if all the connections are made at once, and you're able to cache files more efficiently. If you make a change to one or two files you can just invalidate those caches rather than the cache of your single mega file. Just some thoughts.
>The browser doesn't know if any of the following scripts may depend on the previous ones
Yes it does. That's why the way they're ordered on the page is important. If I include jQuery after I'm trying to make jQuery function calls, it won't work (in all browsers I've tested, anyway).
You didn't get my point, probably because of my terrible english :) The browser has no way of knowing in advance if a script doesn't depend on any of the previous ones, so it cannot optimize this specific case and parse/execute the script before the other ones have been executed. You can manually tell the browser to load the scripts and execute them as soon as they're ready, in no particular order, via the async attribute. If you don't, the browser is going to assume that the order is important and load them one by one.
Comments
AFAIK the scripts cannot be parsed and executed in parallel since they're not explicitly async. The browser doesn't know if any of the following scripts may depend on the previous ones (think jQuery), so it just downloads them and then waits to parse and execute them in order, blocking rendering.
It's true that delivering them in parallel may in some cases reduce the actual download time, but given the small file sizes Apple is serving, the connection overhead (TCP handshake, HTTP headers, slow start, ...) just makes it worse. Most browsers (especially mobile ones) aren't even going to download more than 4-6 files at a time, since they're not using domain sharding.
>It's true that delivering them in parallel may in some cases reduce the actual download time, but given the small file sizes Apple is serving, the connection overhead (TCP handshake, HTTP headers, slow start, ...) just makes it worse. Most browsers (especially mobile ones) aren't even going to download more than 4-6 files at a time, since they're not using domain sharding.
So what I'm wondering is if you target that 4-6 connection limit, if you get all your js files to load in one connection group can you benefit from the parallel downloading while not blocking anything? Like this: http://i.imgur.com/iuriZ.png
Seems to me like the handshake issue goes away if all the connections are made at once, and you're able to cache files more efficiently. If you make a change to one or two files you can just invalidate those caches rather than the cache of your single mega file. Just some thoughts.
>The browser doesn't know if any of the following scripts may depend on the previous ones
Yes it does. That's why the way they're ordered on the page is important. If I include jQuery after I'm trying to make jQuery function calls, it won't work (in all browsers I've tested, anyway).
You didn't get my point, probably because of my terrible english :) The browser has no way of knowing in advance if a script doesn't depend on any of the previous ones, so it cannot optimize this specific case and parse/execute the script before the other ones have been executed. You can manually tell the browser to load the scripts and execute them as soon as they're ready, in no particular order, via the async attribute. If you don't, the browser is going to assume that the order is important and load them one by one.