Grab html element value

How can i grab html element value using php or javascript? I tried using jQuery with DOM ready event, but the problem is that the value that i wanna grab is dynamically loaded from somewhere, and when i use jQuery with DOM ready event most of the times it happens that the DOM is ready but the value of the element is empty (its still not loaded) and when i grab the value with jQuery it gives the empty value of the element, because i am grabbing it before its loaded in the element.

How can i grab the value after its loaded? Is there some kind of trigger or event?

Any help / ideas are appreciated !