Show HN: Cross-browser asynchronous JS script loader w/callbacks

Specifically:

1) the window.onload is being directly overwritten without any chaining. The safe way is to first store a reference to whatever was in .onload beforehand and call that in the overwritten onload.

2) the load check uses an interval on a 10ms timer. Chained setTimeouts are much better for performance and 10ms is quite an aggressive default. 50ms gets called 5x fewer and has a imperceptible difference to the user.

3) _async is some big ol' global var with no function scoping at all.

the problem with this solution is you had to include a blocking js script first to use it... a better solution is to inject your script and for callbacks use an array. Look at how GA.js works, this is all it does, push functions onto an Array (builtin) and once the code loads start pop'ing functions to invoke off the array see: https://gist.github.com/3616965

to make it even better replace the push method on the Array with the invoke method meaning once the code's are loaded - you have immediate invoke of functions... someone should spell this out clearer but it makes me sad to not see this technique used more... it's tiny. see: https://gist.github.com/3616991

updated with two version and formated.

http://labjs.com/

yepnope is an asynchronous conditional resource loader that's super-fast, and allows you to load only the scripts that your users need. 1.7kb minified and gzipped. Check it out!

http://yepnopejs.com/

https://github.com/SlexAxton/yepnope.js

Another Script Loader?#?@$!@# - Why Use Yepnope? - quoting conclusion from the page:

> In short, we want you to make the right decision for your application. We can certainly think of times when yepnope.js would not be the correct choice for a resource loader, and we hope we've made those situations abundantly clear in our documentation. However, we also think that yepnope meets a lot of people where they are, when it comes to a balance of performance, usability, size and feature-set.

> If you have questions about if yepnope is right for your application. Send us a tweet or an email and we'll help you out. Most of us in the script-loader author scene are total BFFs and we aren't about competition, we're about pushing the edge. In other words, we totally use LABjs and RequireJS in a bunch of our projects, because they're badass (and the other ones are probably great too!).

Also, as others have mentioned, there are plenty of options out there, so it might be useful highlight any specific difference or advantage this solution provides over LabJS, RequireJS, Yepnope, curl.js etc

On a side note, there is a rather comprehensive feature matrix of a number of popular JS loaders https://spreadsheets.google.com/lv?key=tDdcrv9wNQRCNCRCflWxh...

https://twitter.com/niftylettuce/status/242946633367683075

[1] http://github.com/iamnoah/writeCapture

https://github.com/hay/jsdynaload

Allows you to do something like this:

jsDynaLoad(['1.js', '2.js', '3.js'], function() { console.log('callback'); });