Can script.readyState be trusted to detect the end of dynamic script loading?

Question

I use dynamic script loading to reduce the duration of the initial page load. To ensure that the functions and objects defined by a script are accessible, I need to ensure t

Answer 1

In Internet Explorer, the onreadystatechange handler fires as expected, after the end of the script.

I performed the same test in Internet Explorer 6, Internet Explorer 7 and Internet Explorer 8, with similar results in these three browsers (here the logs recorded in Internet Explorer 6):

Fri Dec 18 18:14:51 UTC+0100 2009
Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1; .NET CLR 2.0.50727; .NET CLR 3.0.4506.2152; .NET CLR 3.5.30729)
Test for script.readyState behavior started
Added script with onreadystatechange handler
test1.js: Start
test1.js: Start of closure
test1.js: End of closure
readystatechange: complete

Here, with a test using a local file, the readyState is always "complete", and it was still the same after several page refresh.

However, as noted in this post by Nicholas C. Zakas, you may also observe "loaded" and "complete", or just "loaded", under different circumstances.