how to know that an element exists using jQuery code example

Example 1: jquery test div exists

$(document).ready(function() {
    var $myDiv = $('#DivID');

    if ( $myDiv.length){
        //you can now reuse  $myDiv here, without having to select it again.
    }


});

Example 2: jQuery exists function

if ($("#myElementID").length){
   //I exist
}