JSFiddle - React, Tailwind, and code Playground

HTML

<link rel="stylesheet" href="http://ajax.googleapis.com/ajax/libs/jqueryui/1.8/themes/dot-luv/jquery-ui.css">
<form action="" method="post" name="myF" id="myF">
 <input type="text" name="myVal" id="myVal" value="">
 <input type="text" name="myArr" id="myArr" value="">
 <br/>
<input type="submit" name="submit" id="submit" value="go">
</form>

JavaScript

$(function() {
 $("#myVal").blur(function() {
   var arr = $("#myArr").val().split(',');
   if ($.inArray($("#myVal").val(), arr) == -1)
    arr.push($("#myVal").val());
   $("#myArr").val(arr.join(','));
 });
});