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
}

Answer 2

recently I faced the same problem & this is good for me.

if ( $('#para1').lenght == 1 ){ // if the id exists its length will be 1 

      alert('This Id exists');

} elseif ( $('#para1').lenght == 0 ){ // if the id doesn't exists its length will be 0

      alert('This Id does not exists');
}