How to format money on Shopify using JavaScript

I found this Gist for money formatting on Shopify using JavaScript https://gist.github.com/stewartknapman/8d8733ea58d2314c373e94114472d44c

I placed it in my cart page and when I try:

Shopify.formatMoney(2000, '$')

I get this:

cart:2166 Uncaught TypeError: Cannot read property '1' of null
    at Object.Shopify.formatMoney (cart:2166)
    at <anonymous>:1:9

this is at switch(formatString.match(placeholderRegex)[1]) {

I expect to get $20.00

Do you know where the problem is?

Similar question: Shopify Buy Button Error: "cannot read property '1' of null"

The Gist content

var Shopify = Shopify || {};
// ---------------------------------------------------------------------------
// Money format handler
// ---------------------------------------------------------------------------
Shopify.money_format = "${{amount}}";
Shopify.formatMoney = function(cents, format) {
  if (typeof cents == 'string') { cents = cents.replace('.',''); }
  var value = '';
  var placeholderRegex = /{{s*(w+)s*}}/;
  var formatString = (format || this.money_format);

  function defaultOption(opt, def) {
     return (typeof opt == 'undefined' ? def : opt);
  }

  function formatWithDelimiters(number, precision, thousands, decimal) {
    precision = defaultOption(precision, 2);
    thousands = defaultOption(thousands, ',');
    decimal   = defaultOption(decimal, '.');

    if (isNaN(number) || number == null) { return 0; }

    number = (number/100.0).toFixed(precision);

    var parts   = number.split('.'),
        dollars = parts[0].replace(/(d)(?=(ddd)+(?!d))/g, '$1' + thousands),
        cents   = parts[1] ? (decimal + parts[1]) : '';

    return dollars + cents;
  }

  switch(formatString.match(placeholderRegex)[1]) {
    case 'amount':
      value = formatWithDelimiters(cents, 2);
      break;
    case 'amount_no_decimals':
      value = formatWithDelimiters(cents, 0);
      break;
    case 'amount_with_comma_separator':
      value = formatWithDelimiters(cents, 2, '.', ',');
      break;
    case 'amount_no_decimals_with_comma_separator':
      value = formatWithDelimiters(cents, 0, '.', ',');
      break;
  }

  return formatString.replace(placeholderRegex, value);
};