JSFiddle - React, Tailwind, and code Playground

HTML

<link rel="stylesheet" href="http://ajax.googleapis.com/ajax/libs/jqueryui/1.8.4/themes/ui-lightness/jquery-ui.css">

JavaScript

var url = 'youtube.com/watch?v=3sZOD3xKL0Y&feature=youtube_gdata';

url = url.slice( 0, url.indexOf('&') );

alert( url );