@lion/ui/components/localize/src/date/utils/addLeadingZero.js

A package of extendable web components

import { splitDate } from './splitDate.js';
import { pad } from './pad.js';

/**
 * To add a leading zero to a single number
 *
 * @param {string} dateString
 * @returns {string}
 */
export function addLeadingZero(dateString) {
  const dateParts = splitDate(dateString);
  const delimiter = dateParts ? dateParts[2] : '';
  const dateArray =
    dateString.split && dateString.split(delimiter).filter(str => str.trim().length > 0);
  if (!dateArray || dateArray.length !== 3) {
    // prevent fail on invalid dates
    return '';
  }
  return dateArray.map(pad).join('-');
}