Javascript - var being used in another var?

Question

why do some people store a var within another var?

For example:

var checked = $("#filterControls :checkbox:checked");
var arr = checked

A more expansive view of the code below.

var checked = $("#filterControls :checkbox:checked");
if (checked.length) {
  rows.hide(200);
  var arr = checked
    .map(function() {
      return "." + $(this).val();
    })
    .get();
  var selector = arr.join("");
  $(selector).show(200);
}

Answer 1

You got a wrong idea about the map function. The map function is immutable, but it returns the modified entries. Because of that you have to assign it to a new value. So checked has the unmodifed values and arr has the values which were modified by map -function.