date format validation

DateFormatValidation.js

const testone = require('@fedeghe/testone');

const validDate = value => {
    const plainValue = value.replace(/[^\d]/g, ' ');
    const elements = plainValue.split(/\s/).map(i => parseInt(i, 10));
    // must find month < 13
    const foundMonth = elements.findIndex(e => e > 0 && e < 13);
    if (foundMonth < 0) return false;
  	// must find another value in [1,31]
	const foundDate = elements.findIndex(
      (e,i) => i != foundMonth && e > 0 && e < 32
    );
    if (foundDate < 0) return false;
	// finally must find a YYYY
	const foundYear = elements.findIndex(e => e >= 1e3 && e < 1e4);
    if (foundYear < 0) return false;
	// still the date could be invalid (non leap e.g.) 2011-02-31
	const d = new Date(plainValue),
          t = d.setHours(0);
    d.setMinutes(0);
    d.setSeconds(0);
    d.setMilliseconds(0);
  	return d.getFullYear() === elements[foundYear] &&
      d.getMonth()+1 === elements[foundMonth] &&
      d.getDate() === elements[foundDate];
};
testone([
  { in: ['2020-12-12'], out: true},
  { in: ['2020-12-31'], out: true},
  { in: ['2023-01-01'], out: true},
  //
  { in: ['2020-12-32'], out: false},
  { in: ['2020-13-13'], out: false},
  { in: ['2020-13-13'], out: false},
  { in: ['2020-00-13'], out: false},
  { in: ['999-12-13'], out: false},
  { in: ['10000-12-13'], out: false},
  { in: ['0-12-13'], out: false},
], validDate).then(res => {
  console.log({validDate: res.passing})
})

const validFormat = (format, allowedSep, els = ['YYYY', 'MM', 'DD']) => {
  const hasEls = els.every(el => format.includes(el)),
        sep = format.replace(/\w/g, '').split('');
  let sepOk = true;
  if (allowedSep) sep.forEach(s => {
    sepOk &&= allowedSep.includes(s);
  });
  return sepOk && sep.length === els.length-1 &&
    !!hasEls;
};
testone([
  { in: ['YYYY-MM-DD'], out: true},
  { in: ['YYYY-MM-DD', ['-']], out: true},
  { in: ['MM-DD', ['-'], ['MM', 'DD']], out: true},
  { in: ['YYYY/DD', ['/'], ['YYYY', 'DD']], out: true},
  //
  { in: ['YYYY-MM-DD', [';']], out: false},
  { in: ['2020-13-13'], out: false},
  { in: ['MM/DD', ['-'], ['MM', 'DD']], out: false},
], validFormat).then(res => {
  console.log({validFormat: res.passing})
});

function isValidDate(dateString, format, separators, placeholders) {
    // Escape special characters in a string for use in a regex
    function escapeRegex(str) {
        return str.replace(/[-\/\\^$*+?.()|[\]{}]/g, '\\$&');
    }

    // Create a regex pattern to match the date format
    let separatorPattern = separators.map(escapeRegex).join('|');
    let placeholderPattern = placeholders.map(escapeRegex).join('|');

    // Split the format into components
    let formatComponents = format.split(new RegExp(`(${separatorPattern}|${placeholderPattern})`));

    // Build the regex pattern based on the format components
    let regexPattern = formatComponents.map(component => {
        switch (component) {
            case 'DD':
                return '(\\d{2})';
            case 'MM':
                return '(\\d{2})';
            case 'YYYY':
                return '(\\d{4})';
            case 'YY':
                return '(\\d{2})';
            default:
                return escapeRegex(component);
        }
    }).join('');

    let dateRegex = new RegExp(`^${regexPattern}$`);
    let match = dateString.match(dateRegex);

    if (!match) {
        return false;
    }

    // Extract the date components from the match
    let dateComponents = {};
    let formatIndex = 1;

    formatComponents.forEach(component => {
        if (component === 'DD' || component === 'MM' || component === 'YYYY' || component === 'YY') {
            dateComponents[component] = match[formatIndex++];
        }
    });

    let day = parseInt(dateComponents['DD'], 10);
    let month = parseInt(dateComponents['MM'], 10) - 1; // Months are zero-indexed in JavaScript Date
    let year = parseInt(dateComponents['YYYY'] || `20${dateComponents['YY']}`, 10);

    // Validate the date by creating a Date object and checking its components
    let date = new Date(year, month, day);
    return date.getFullYear() === year && date.getMonth() === month && date.getDate() === day;
}

// Example usage:
let dateString = "12-05-2024";
let format = "DD-MM-YYYY";
let separators = ['-', '/'];
let placeholders = [' '];

console.log(isValidDate(dateString, format, separators, placeholders)); // Output: true