Finding whether the element exists in whole html page

Question

I want to check whether an element exists in the whole page or not. Is there any way to know if the element exists in the page through jQuery?

For example:

Answer 1

For element IDs:

if($('#para1').length){
  //element with id exists
}

For element class:

if($('.para_class').length){
  //element with class exists
}