 <p>You can use the <code>format</code> option:</p> <pre><code>// Move formatting code into a function function toFormat ( v ) { return formatDate(new Date(v)); } // Add a formatter to the slider format: { to: toFormat, from: Number } // You can then directly use the value in the update function dateValues[handle].innerHTML = values[handle]; </code></pre> <p>Updated <a href="https://jsfiddle.net/leongersen/vvgr74v2/1/" rel="nofollow">fiddle</a>.</p>