JSFiddle - React, Tailwind, and code Playground
HTML
<ul>
<li id="foo">foo</li>
<li id="bar">bar</li>
<li id="baz">baz</li>
</ul>
JavaScript
var listItem = $( " " );
alert( $( "li" ).index( listItem ) );
<ul>
<li id="foo">foo</li>
<li id="bar">bar</li>
<li id="baz">baz</li>
</ul>
var listItem = $( " " );
alert( $( "li" ).index( listItem ) );