JavaScript::Validating a date effectively

Validating a date effectively

function isValidDate(value, userFormat) {

  // Set default format if format is not provided

  userFormat = userFormat || 'mm/dd/yyyy';

  // Find custom delimiter by excluding

  // month, day and year characters

  var delimiter = /[^mdy]/.exec(userFormat)[0];

  // Create an array with month, day and year

  // so we know the format order by index

  var theFormat = userFormat.split(delimiter);

  // Create array from user date

  var theDate = value.split(delimiter);

  function isDate(date, format) {

    var m, d, y, i = 0, len = format.length, f;

    for (i; i < len; i++) {

      f = format[i];

      if (/m/.test(f)) m = date[i];

      if (/d/.test(f)) d = date[i];

      if (/y/.test(f)) y = date[i];

    }

    return (

      m > 0 && m < 13 &&

      y && y.length === 4 &&

      d > 0 &&

      // Check if it's a valid day of the month

      d <= (new Date(y, m, 0)).getDate()

    );

  }

  return isDate(theDate, theFormat);

}

The date library in JavaScript is often too simple and usually not enough for advanced date formatting. Although there are many JS libraries that make working with dates much easier, sometimes you just want something simple that validates a date from a string. In that case you can use the following script. It lets you validate a date with any delimiter character and 4 digit year.