String is ISO formatted date

Checks if the given string is valid in the simplified extended ISO format (ISO 8601).

• Use the Date constructor to create a Date object from the given string.
• Use Date.prototype.valueOf() and Number.isNaN() to check if the produced date object is valid.
• Use Date.prototype.toISOString() to compare the ISO formatted string representation of the date with the original string.

const isISOString = val => {
  const d = new Date(val);
  return !Number.isNaN(d.valueOf()) && d.toISOString() === val;
};

isISOString('2020-10-12T10:10:10.000Z'); // true
isISOString('2020-10-12'); // false