What are the essential functions you always use in javascript and jquery ?

Ajax Calls and configuring caching and async as this the mmost common settings you need to be aware of.

Also the events bindings for dynamic controls using on or live depends on the version of jQuery when it comes to dynamic controls as it is different from the control built within the page.

Also the Graphical effect such as animate and accordion for jQuery UI

Selectors, events, and ajax request ( to make your site dynamic and not reload your page ).

onclick();

onchange();

onkeydown();

onkeypressed();

onkeyup();

onclick()

ondrag()

etc