JSFiddle - React, Tailwind, and code Playground

HTML

<input type="text" id="GiftPurchase_recipient_first_name"/>
<input type="text" id="GiftPurchase_recipient_last_name"/>

<input type="text" id="gift_to"/>

JavaScript

$(document).ready(function(){
    $('#GiftPurchase_recipient_first_name,#GiftPurchase_recipient_last_name').bind('blur',function(){
        var gift_to  = $('#GiftPurchase_recipient_first_name').val()+" "+$('#GiftPurchase_recipient_last_name').val();
        $("#gift_to").val(gift_to);
    });
});