There are prehtml posthtml prejs postjs JavaScript events on select pages.
The prejs and postjs events are for the running of the JS not for the loading of scripts by the browser.
There can me multiple postjs events as it's triggered after any ajax that adds to the page.
Nothing other than custom scripts listen for these events.

Usage example:

function my_method(){alert("hello world");}
top.noodle.cbc.addEventListener(top.document.getElementById('main'), 'postjs', my_method);

or if you are using IE:

function my_method(e){if(e.noodle=="postjs"){alert("hello world");}}
top.noodle.cbc.addEventListener(top.document.getElementById('main'), 'propertychange', my_method);