Its gives better performance to use a javascript object than it does to use a jQuery selector.

use-js-objects-for-performance.js

var el = document.getElementById('header'); // this is for #header not <header>

$(el).('.some-class-used-in-header').each(function(index){
  // do something!! to each of the things with this class
});

$(el.getElementsByTagName('nav')).on('touchstart click', 'a', function(e){
    // do something when an <A> inside a <NAV> inside #header is  clicked.
    e.preventDefault();  // prevents the default click action
});