DOM traversal methods

The jQuery selectors that we have explored so far allow us to select a set of elements as we navigate across and down the DOM tree and filter the results. If this were the only way to select elements, our options would be somewhat limited. There are many occasions when selecting a parent or ancestor element is essential; that is where jQuery's DOM traversal methods come into play. With these methods, we can go up, down, and all around the DOM tree with ease.

Some of the methods have a nearly identical counterpart among the selector expressions. For example, the line we first used to add the alt class, $('tr:even').addClass('alt'), could be rewritten with the .filter() method as follows:

$('tr')
  .filter(':even')
  .addClass('alt'); 

For the most part, however, the two ways of selecting elements complement each other. Also, the .filter() method in particular has enormous power because it can take a function as its argument. The function allows us to create complex tests...