JSFiddle - React, Tailwind, and code Playground

HTML

<link rel="stylesheet" href="http://getbootstrap.com/dist/css/bootstrap.min.css">
<div class="container">
    <div class="page-header">
        <h1>Date/Time Formatting with JS</h1>
    </div>
    <p class="lead">To get started, enter a date time in the input box below and click <strong>Convert</strong>.</p>
    
    <div class="row">
        <div class="col-xs-8">
            <input type="datetime-local" class="form-control" id="datetime"/>
        </div>
        <div class="col-xs-4">
            <input type="submit" class="btn btn-primary" value="Convert"/>
        </div>
    </div>
    <hr>
    <div class="row">
        <div class="col-xs-2"><label>Output</label></div>
        <div class="col-xs-10"><pre id="output"></pre></div>
    </div>
</div>

JavaScript

function toDateTime(date) {
    var str = '';
    var year, month, day, hour, min;
    year = date.getUTCFullYear();
    month = date.getUTCMonth() + 1;
    month = month < 10 ? '0' + month : month;
    day = date.getUTCDate();
    day = day < 10 ? '0' + day : day;
    hour = date.getUTCHours();
    hour = hour < 10 ? '0' + hour : hour;
    min = date.getUTCMinutes();
    min = min < 10 ? '0' + min : min;
    
    str += year + '-' + month + '-' + day;
    str += ' ' + hour + ':' + min;
    return str;
}

$('[type=submit]').click(function(e) {
    var $input = $('#datetime');
    var value = $input.val();
    var date = new Date(value);
    var ts = toDateTime(date);
    $('#output').html(ts);
});