code: function numberFormat(number, decimals, decPoint, thousandsSep) {
          var externalFn = Highcharts.numberFormat,
            lang = defaultOptions.lang,
          // http://kevin.vanzonneveld.net/techblog/article/javascript_equivalent_for_phps_number_format/
            n = +number || 0,
            c = decimals === -1 ?
              (n.toString().split('.')[1] || '').length : // preserve decimals
              (isNaN(decimals = mathAbs(decimals)) ? 2 : decimals),
            d = decPoint === undefined ? lang.decimalPoint : decPoint,
            t = thousandsSep === undefined ? lang.thousandsSep : thousandsSep,
            s = n < 0 ? "-" : "",
            i = String(pInt(n = mathAbs(n).toFixed(c))),
            j = i.length > 3 ? i.length % 3 : 0;
  
          return externalFn !== numberFormat ?
            externalFn(number, decimals, decPoint, thousandsSep) :
            (s + (j ? i.substr(0, j) + t : "") + i.substr(j).replace(/(\d{3})(?=\d)/g, "$1" + t) +
            (c ? d + mathAbs(n - i).toFixed(c).slice(2) : ""));
      }
docs: Format a number and return a string based on input settings
  @param {Number} number The input number to format
  @param {Number} decimals The amount of decimals
  @param {String} decPoint The decimal point, defaults to the one given in the lang options
  @param {String} thousandsSep The thousands separator, defaults to the one given in the lang options