Useful jQuery .eq() method

I want to mark a specific li tag in the ul, the HTML code is like this:

<ul>
  <li>li-1</li>
  <li>li-2</li>
  <li>li-3</li>
  <li>li-4</li>
</ul>

In order to mark it, I used .data() method in the jQuery, just like this:

$( 'ul' ).data('show',1);

How to find the specific li tag?

I just use the JavaScript Array method:

$('li')[2].data('show',1);

but I get the error info:

undefined is not a function.

Why? when you use [] method to get the $’s result, it’s not a jQuery object, but a JavaScript Dom object. So how to get the jQuery object? There’s two method:

Use $()

The first method is using $() method to cover the [] result, like this

$( $('li')[2] ).data('show',1);

Use .eq() method

The second method is using jQuery method .eq(), you can write like this

$('li').eq(2).data('show',1);