JSFiddle - React, Tailwind, and code Playground

HTML

<script src="http://ajax.microsoft.com/ajax/jquery.validate/1.7/jquery.validate.js"></script>
<link rel="stylesheet" href="http://ajax.googleapis.com/ajax/libs/jqueryui/1.8.4/themes/ui-lightness/jquery-ui.css">

JavaScript

var list = [1,2,3, 6,7,8];
var pos = 3;
var tasks = [4,5];

var newlist = list.slice(0,pos).concat(tasks,list.slice(pos));


alert(newlist);