LOL.

The Javascript engine you are running in the Pronto is circa 2008 (EcmaScript 5 - ES5) which is way before padStart was added to String.

You must resort to the old way or adding what is known as a mixin
or polyfills.

Old way:

var toPad = 1;
var padded = ("00" + toPad).substring(0,2);


A quick google (string padstart polyfill) finds this link which has exactly what you need. [Link: vanillajstoolkit.com]

If you look at this code, however, it's also looking for a 'repeat' function on String which also is not part of ES5.

Here's a link for that:

[Link: vanillajstoolkit.com]