I want to validate the date format on an input using the format mm/dd/yyyy.

I found below codes in one site and then used it but it doesn't work:

function isDate(ExpiryDate) { 
    var objDate,  // date object initialized from the ExpiryDate string 
        mSeconds, // ExpiryDate in milliseconds 
        day,      // day 
        month,    // month 
        year;     // year 
    // date length should be 10 characters (no more 开发者_如何学Pythonno less) 
    if (ExpiryDate.length !== 10) { 
        return false; 
    } 
    // third and sixth character should be '/' 
    if (ExpiryDate.substring(2, 3) !== '/' || ExpiryDate.substring(5, 6) !== '/') { 
        return false; 
    } 
    // extract month, day and year from the ExpiryDate (expected format is mm/dd/yyyy) 
    // subtraction will cast variables to integer implicitly (needed 
    // for !== comparing) 
    month = ExpiryDate.substring(0, 2) - 1; // because months in JS start from 0 
    day = ExpiryDate.substring(3, 5) - 0; 
    year = ExpiryDate.substring(6, 10) - 0; 
    // test year range 
    if (year < 1000 || year > 3000) { 
        return false; 
    } 
    // convert ExpiryDate to milliseconds 
    mSeconds = (new Date(year, month, day)).getTime(); 
    // initialize Date() object from calculated milliseconds 
    objDate = new Date(); 
    objDate.setTime(mSeconds); 
    // compare input date and parts from Date() object 
    // if difference exists then date isn't valid 
    if (objDate.getFullYear() !== year || 
        objDate.getMonth() !== month || 
        objDate.getDate() !== day) { 
        return false; 
    } 
    // otherwise return true 
    return true; 
}

function checkDate(){ 
    // define date string to test 
    var ExpiryDate = document.getElementById(' ExpiryDate').value; 
    // check date and print message 
    if (isDate(ExpiryDate)) { 
        alert('OK'); 
    } 
    else { 
        alert('Invalid date format!'); 
    } 
}

Any suggestion about what could be wrong?

I think Niklas has the right answer to your problem. Besides that, I think the following date validation function is a little bit easier to read:

// Validates that the input string is a valid date formatted as "mm/dd/yyyy"
function isValidDate(dateString)
{
    // First check for the pattern
    if(!/^\d{1,2}\/\d{1,2}\/\d{4}$/.test(dateString))
        return false;

    // Parse the date parts to integers
    var parts = dateString.split("/");
    var day = parseInt(parts[1], 10);
    var month = parseInt(parts[0], 10);
    var year = parseInt(parts[2], 10);

    // Check the ranges of month and year
    if(year < 1000 || year > 3000 || month == 0 || month > 12)
        return false;

    var monthLength = [ 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 ];

    // Adjust for leap years
    if(year % 400 == 0 || (year % 100 != 0 && year % 4 == 0))
        monthLength[1] = 29;

    // Check the range of the day
    return day > 0 && day <= monthLength[month - 1];
};

I would use Moment.js for date validation.

alert(moment("05/22/2012", 'MM/DD/YYYY',true).isValid()); //true

Jsfiddle: http://jsfiddle.net/q8y9nbu5/

true value is for strict parsing credit to @Andrey Prokhorov which means

you may specify a boolean for the last argument to make Moment use strict parsing. Strict parsing requires that the format and input match exactly, including delimeters.

Use the following regular expression to validate:

var date_regex = /^(0[1-9]|1[0-2])\/(0[1-9]|1\d|2\d|3[01])\/(19|20)\d{2}$/;
if (!(date_regex.test(testDate))) {
    return false;
}

This is working for me for MM/dd/yyyy.

All credits go to elian-ebbing

Just for the lazy ones here I also provide a customized version of the function for the format yyyy-mm-dd.

function isValidDate(dateString)
{
    // First check for the pattern
    var regex_date = /^\d{4}\-\d{1,2}\-\d{1,2}$/;

    if(!regex_date.test(dateString))
    {
        return false;
    }

    // Parse the date parts to integers
    var parts   = dateString.split("-");
    var day     = parseInt(parts[2], 10);
    var month   = parseInt(parts[1], 10);
    var year    = parseInt(parts[0], 10);

    // Check the ranges of month and year
    if(year < 1000 || year > 3000 || month == 0 || month > 12)
    {
        return false;
    }

    var monthLength = [ 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 ];

    // Adjust for leap years
    if(year % 400 == 0 || (year % 100 != 0 && year % 4 == 0))
    {
        monthLength[1] = 29;
    }

    // Check the range of the day
    return day > 0 && day <= monthLength[month - 1];
}

It's unusual to see a post so old on such a basic topic, with so many answers, none of them right. (I'm not saying none of them work.)

A leap-year determination routine is not needed for this. The language can do that work for us.
Moment is not needed for this.
Date.parse() shouldn't be used for local date strings. MDN says "It is not recommended to use Date.parse as until ES5, parsing of strings was entirely implementation dependent." The standard requires a (potentially simplified) ISO 8601 string; support for any other format is implementation-dependent.
Nor should new Date(string) be used, because that uses Date.parse().
IMO the leap day should be validated.
The validation function must account for the possibility that the input string doesn't match the expected format. For example, '1a/2a/3aaa', '1234567890', or 'ab/cd/efgh'.

Here's an efficient, concise solution with no implicit conversions. It takes advantage of the Date constructor's willingness to interpret 2018-14-29 as 2019-03-01. It does use a couple modern language features, but those are easily removed if needed. I've also included some tests.

function isValidDate(s) {
  // Assumes s is "mm/dd/yyyy"
  if (!/^\d\d\/\d\d\/\d\d\d\d$/.test(s)) {
    return false;
  }
  const parts = s.split('/').map((p) => parseInt(p, 10));
  parts[0] -= 1;
  const d = new Date(parts[2], parts[0], parts[1]);
  return d.getMonth() === parts[0] && d.getDate() === parts[1] && d.getFullYear() === parts[2];
}

function testValidDate(s) {
  console.log(s, isValidDate(s));
}
testValidDate('01/01/2020'); // true
testValidDate('02/29/2020'); // true
testValidDate('02/29/2000'); // true
testValidDate('02/29/1900'); // false
testValidDate('02/29/2019'); // false
testValidDate('01/32/1970'); // false
testValidDate('13/01/1970'); // false
testValidDate('14/29/2018'); // false
testValidDate('1a/2b/3ccc'); // false
testValidDate('1234567890'); // false
testValidDate('aa/bb/cccc'); // false
testValidDate(null); // false
testValidDate(''); // false

You could use Date.parse()

You can read in MDN documentation

The Date.parse() method parses a string representation of a date, and returns the number of milliseconds since January 1, 1970, 00:00:00 UTC or NaN if the string is unrecognized or, in some cases, contains illegal date values (e.g. 2015-02-31).

And check if the result of Date.parse isNaN

let isValidDate = Date.parse('01/29/1980');

if (isNaN(isValidDate)) {
  // when is not valid date logic

  return false;
}

// when is valid date logic

Please take a look when is recommended to use Date.parse in MDN

It appears to be working fine for mm/dd/yyyy format dates, example:

http://jsfiddle.net/niklasvh/xfrLm/

The only problem I had with your code was the fact that:

var ExpiryDate = document.getElementById(' ExpiryDate').value;

Had a space inside the brackets, before the element ID. Changed it to:

var ExpiryDate = document.getElementById('ExpiryDate').value;

Without any further details regarding the type of data that isn't working, there isn't much else to give input on.

The function will return true if the given string is in the right format('MM/DD/YYYY') else it will return false. (I found this code online & modified it a little)

function isValidDate(date) {
    var temp = date.split('/');
    var d = new Date(temp[2] + '/' + temp[0] + '/' + temp[1]);
    return (d && (d.getMonth() + 1) == temp[0] && d.getDate() == Number(temp[1]) && d.getFullYear() == Number(temp[2]));
}

console.log(isValidDate('02/28/2015'));

It's ok if you want to check validate dd/MM/yyyy

function isValidDate(date) {
    var temp = date.split('/');
    var d = new Date(temp[1] + '/' + temp[0] + '/' + temp[2]);
     return (d && (d.getMonth() + 1) == temp[1] && d.getDate() == Number(temp[0]) && d.getFullYear() == Number(temp[2]));
}

alert(isValidDate('29/02/2015')); // it not exist ---> false

Expanding (or better contracting) on @Jay Dunnings answer, the following two-liner uses the Intl API and ES6 destructuring. It passes all tests given by Jay Dunning.

/**
 * @param {string} date
 * @returns {boolean} true if date is of the form mm/dd/yyyy
 */
function is_en_US_date(date) {
    const [match, mm, dd, yyyy] = /^(\d\d)[/](\d\d)[/](\d{4})$/.exec(date) || [];
    return match !== undefined && new Intl.DateTimeFormat('en-US', { month: '2-digit', day: '2-digit', year: 'numeric' }).format(new Date(yyyy, mm-1, dd)) === date
}

Here is one snippet to check for valid date:

function validateDate(dateStr) {
   const regExp = /^(\d\d?)\/(\d\d?)\/(\d{4})$/;
   let matches = dateStr.match(regExp);
   let isValid = matches;
   let maxDate = [0, 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31];
   
   if (matches) {
     const month = parseInt(matches[1]);
     const date = parseInt(matches[2]);
     const year = parseInt(matches[3]);
     
     isValid = month <= 12 && month > 0;
     isValid &= date <= maxDate[month] && date > 0;
     
     const leapYear = (year % 400 == 0)
        || (year % 4 == 0 && year % 100 != 0);
     isValid &= month != 2 || leapYear || date <= 28; 
   }
   
   return isValid
}

console.log(['1/1/2017', '01/1/2017', '1/01/2017', '01/01/2017', '13/12/2017', '13/13/2017', '12/35/2017'].map(validateDate));

Alternative

This question has already been answered ad nauseum, I know, but I'd like to throw myself to the SO wolves by proposing an alternative solution.

AFAICT, this method isn't presented in any of the other answers. And maybe there's some edge case that I'm not considering... I'm sure y'all will duly roast me if so.

Someone once said-- Jesus or Confucius, maybe --

When you decide to solve a problem with regex, now you have two problems

That said, I love regex and use it on a regular basis for other things; however, recently, I ran into an issue with one of the top answers on here, which threw a false positive for an invalid date. It used too strict a regex. I replaced said check of a date string (dd/dd/dddd) with the following:

const isInvalidDate = (dateString) => new Date(dateString).toString() === 'Invalid Date'

console.log(isInvalidDate('asdf')) //> true
console.log(isInvalidDate('09/29/1985')) //> false

Edit 2022

My alternative solution remains the same since I posted it, but it could perhaps be better written in a non-negative-ish form to minimize cognitive strain. So, if you're gonna copy-paste it, copy-paste this instead:

const isValidDate = (dateString) => new Date(dateString).toString() !== 'Invalid Date'

console.log(isValidDate('asdf')) //> false
console.log(isValidDate('09/29/1985')) //> true

Why am I still talking?

As @jay-dunning points out above, this solution may not be ideal for some applications (presumably those implemented in <ES5? cough). I'm not at all compelled to stop using my solution, but just beware:

Date.parse() shouldn't be used for local date strings. MDN says "It is not recommended to use Date.parse as until ES5, parsing of strings was entirely implementation dependent." The standard requires a
(potentially simplified) ISO 8601 string; support for any other
format is implementation-dependent.

Nor should new Date(string) be used, because that uses Date.parse().

Moment is really a good one to resolve it. I don't see reason to add complexity just to check date... take a look on moment : http://momentjs.com/

HTML :

<input class="form-control" id="date" name="date" onchange="isValidDate(this);" placeholder="DD/MM/YYYY" type="text" value="">

Script :

 function isValidDate(dateString)  {
    var dateToValidate = dateString.value
    var isValid = moment(dateToValidate, 'MM/DD/YYYY',true).isValid()
    if (isValid) {
        dateString.style.backgroundColor = '#FFFFFF';
    } else {
        dateString.style.backgroundColor = '#fba';
    }   
};

Find in the below code which enables to perform the date validation for any of the supplied format to validate start/from and end/to dates. There could be some better approaches but have come up with this. Note supplied date format and date string go hand in hand.

function validate() {

  var format = 'yyyy-MM-dd';

  if (isAfterCurrentDate(document.getElementById('start').value, format)) {
    console.log('Date is after the current date.');
  } else {
    console.log('Date is not after the current date.');
  }
  if (isBeforeCurrentDate(document.getElementById('start').value, format)) {
    console.log('Date is before current date.');
  } else {
    console.log('Date is not before current date.');
  }
  if (isCurrentDate(document.getElementById('start').value, format)) {
    console.log('Date is current date.');
  } else {
    console.log('Date is not a current date.');
  }
  if (isBefore(document.getElementById('start').value, document.getElementById('end').value, format)) {
    console.log('Start/Effective Date cannot be greater than End/Expiration Date');
  } else {
    console.log('Valid dates...');
  }
  if (isAfter(document.getElementById('start').value, document.getElementById('end').value, format)) {
    console.log('End/Expiration Date cannot be less than Start/Effective Date');
  } else {
    console.log('Valid dates...');
  }
  if (isEquals(document.getElementById('start').value, document.getElementById('end').value, format)) {
    console.log('Dates are equals...');
  } else {
    console.log('Dates are not equals...');
  }
  if (isDate(document.getElementById('start').value, format)) {
    console.log('Is valid date...');
  } else {
    console.log('Is invalid date...');
  }
}

/**
 * This method gets the year index from the supplied format
 */
function getYearIndex(format) {

  var tokens = splitDateFormat(format);

  if (tokens[0] === 'YYYY' ||
    tokens[0] === 'yyyy') {
    return 0;
  } else if (tokens[1] === 'YYYY' ||
    tokens[1] === 'yyyy') {
    return 1;
  } else if (tokens[2] === 'YYYY' ||
    tokens[2] === 'yyyy') {
    return 2;
  }
  // Returning the default value as -1
  return -1;
}

/**
 * This method returns the year string located at the supplied index
 */
function getYear(date, index) {

  var tokens = splitDateFormat(date);
  return tokens[index];
}

/**
 * This method gets the month index from the supplied format
 */
function getMonthIndex(format) {

  var tokens = splitDateFormat(format);

  if (tokens[0] === 'MM' ||
    tokens[0] === 'mm') {
    return 0;
  } else if (tokens[1] === 'MM' ||
    tokens[1] === 'mm') {
    return 1;
  } else if (tokens[2] === 'MM' ||
    tokens[2] === 'mm') {
    return 2;
  }
  // Returning the default value as -1
  return -1;
}

/**
 * This method returns the month string located at the supplied index
 */
function getMonth(date, index) {

  var tokens = splitDateFormat(date);
  return tokens[index];
}

/**
 * This method gets the date index from the supplied format
 */
function getDateIndex(format) {

  var tokens = splitDateFormat(format);

  if (tokens[0] === 'DD' ||
    tokens[0] === 'dd') {
    return 0;
  } else if (tokens[1] === 'DD' ||
    tokens[1] === 'dd') {
    return 1;
  } else if (tokens[2] === 'DD' ||
    tokens[2] === 'dd') {
    return 2;
  }
  // Returning the default value as -1
  return -1;
}

/**
 * This method returns the date string located at the supplied index
 */
function getDate(date, index) {

  var tokens = splitDateFormat(date);
  return tokens[index];
}

/**
 * This method returns true if date1 is before date2 else return false
 */
function isBefore(date1, date2, format) {
  // Validating if date1 date is greater than the date2 date
  if (new Date(getYear(date1, getYearIndex(format)),
      getMonth(date1, getMonthIndex(format)) - 1,
      getDate(date1, getDateIndex(format))).getTime() >
    new Date(getYear(date2, getYearIndex(format)),
      getMonth(date2, getMonthIndex(format)) - 1,
      getDate(date2, getDateIndex(format))).getTime()) {
    return true;
  }
  return false;
}

/**
 * This method returns true if date1 is after date2 else return false
 */
function isAfter(date1, date2, format) {
  // Validating if date2 date is less than the date1 date
  if (new Date(getYear(date2, getYearIndex(format)),
      getMonth(date2, getMonthIndex(format)) - 1,
      getDate(date2, getDateIndex(format))).getTime() <
    new Date(getYear(date1, getYearIndex(format)),
      getMonth(date1, getMonthIndex(format)) - 1,
      getDate(date1, getDateIndex(format))).getTime()
  ) {
    return true;
  }
  return false;
}

/**
 * This method returns true if date1 is equals to date2 else return false
 */
function isEquals(date1, date2, format) {
  // Validating if date1 date is equals to the date2 date
  if (new Date(getYear(date1, getYearIndex(format)),
      getMonth(date1, getMonthIndex(format)) - 1,
      getDate(date1, getDateIndex(format))).getTime() ===
    new Date(getYear(date2, getYearIndex(format)),
      getMonth(date2, getMonthIndex(format)) - 1,
      getDate(date2, getDateIndex(format))).getTime()) {
    return true;
  }
  return false;
}

/**
 * This method validates and returns true if the supplied date is 
 * equals to the current date.
 */
function isCurrentDate(date, format) {
  // Validating if the supplied date is the current date
  if (new Date(getYear(date, getYearIndex(format)),
      getMonth(date, getMonthIndex(format)) - 1,
      getDate(date, getDateIndex(format))).getTime() ===
    new Date(new Date().getFullYear(),
      new Date().getMonth(),
      new Date().getDate()).getTime()) {
    return true;
  }
  return false;
}

/**
 * This method validates and returns true if the supplied date value 
 * is before the current date.
 */
function isBeforeCurrentDate(date, format) {
  // Validating if the supplied date is before the current date
  if (new Date(getYear(date, getYearIndex(format)),
      getMonth(date, getMonthIndex(format)) - 1,
      getDate(date, getDateIndex(format))).getTime() <
    new Date(new Date().getFullYear(),
      new Date().getMonth(),
      new Date().getDate()).getTime()) {
    return true;
  }
  return false;
}

/**
 * This method validates and returns true if the supplied date value 
 * is after the current date.
 */
function isAfterCurrentDate(date, format) {
  // Validating if the supplied date is before the current date
  if (new Date(getYear(date, getYearIndex(format)),
      getMonth(date, getMonthIndex(format)) - 1,
      getDate(date, getDateIndex(format))).getTime() >
    new Date(new Date().getFullYear(),
      new Date().getMonth(),
      new Date().getDate()).getTime()) {
    return true;
  }
  return false;
}

/**
 * This method splits the supplied date OR format based 
 * on non alpha numeric characters in the supplied string.
 */
function splitDateFormat(dateFormat) {
  // Spliting the supplied string based on non characters
  return dateFormat.split(/\W/);
}

/*
 * This method validates if the supplied value is a valid date.
 */
function isDate(date, format) {
  // Validating if the supplied date string is valid and not a NaN (Not a Number)
  if (!isNaN(new Date(getYear(date, getYearIndex(format)),
      getMonth(date, getMonthIndex(format)) - 1,
      getDate(date, getDateIndex(format))))) {
    return true;
  }
  return false;
}

<input type="text" name="start" id="start" size="10" value="" />
<br/>
<input type="text" name="end" id="end" size="10" value="" />
<br/>
<input type="button" value="Submit" onclick="validate();" />

function fdate_validate(vi)
{
  var parts =vi.split('/');
  var result;
  var mydate = new Date(parts[2],parts[1]-1,parts[0]);
  if (parts[2] == mydate.getYear() && parts[1]-1 == mydate.getMonth() && parts[0] == mydate.getDate() )
  {result=0;}
  else
  {result=1;}
  return(result);
}

Date is complex. The best way to validate it is using package like Luxon , date-fns, or DayJS.

Using date-fns:

import {isMatch} from 'date-fns'

const match = isMatch('12/25/2010', 'MM/dd/yyyy') // true

Similar to Elian Ebbing answer, but support "\", "/", ".", "-", " " delimiters

function js_validate_date_dmyyyy(js_datestr)
{
    var js_days_in_year = [ 0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 ];
    var js_datepattern = /^(\d{1,2})([\.\-\/\\ ])(\d{1,2})([\.\-\/\\ ])(\d{4})$/;

    if (! js_datepattern.test(js_datestr)) { return false; }

    var js_match = js_datestr.match(js_datepattern);
    var js_day = parseInt(js_match[1]);
    var js_delimiter1 = js_match[2];
    var js_month = parseInt(js_match[3]);
    var js_delimiter2 = js_match[4];
    var js_year = parseInt(js_match[5]);                            

    if (js_is_leap_year(js_year)) { js_days_in_year[2] = 29; }

    if (js_delimiter1 !== js_delimiter2) { return false; } 
    if (js_month === 0  ||  js_month > 12)  { return false; } 
    if (js_day === 0  ||  js_day > js_days_in_year[js_month])   { return false; } 

    return true;
}

function js_is_leap_year(js_year)
{ 
    if(js_year % 4 === 0)
    { 
        if(js_year % 100 === 0)
        { 
            if(js_year % 400 === 0)
            { 
                return true; 
            } 
            else return false; 
        } 
        else return true; 
    } 
    return false; 
}

Javascript

function validateDate(date) {
    try {
        new Date(date).toISOString();
        return true;
    } catch (e) { 
        return false; 
    }
}

JQuery

$.fn.validateDate = function() {
    try {
        new Date($(this[0]).val()).toISOString();
        return true;
    } catch (e) { 
        return false; 
    }
}

returns true for a valid date string.

we can use customized function or date pattern. Below code is customized function as per your requirement please change it.

 function isValidDate(str, separator = '-') {
    var getvalue = str.split(separator);
    var day = parseInt(getvalue[2]);
    var month = parseInt(getvalue[1]);
    var year = parseInt(getvalue[0]);
    if(year < 1901 || year > 2100){
       return false;
    }
    if (month < 1 || month > 12) { 
       return false;
    }
    if (day < 1 || day > 31) {
       return false;
    }
    if ((month==4 && month==6 && month==9 && month==11) && day==31) {
       return false;
    }
    if (month == 2) { // check for february 29th
       var isleap = (year % 4 == 0 && (year % 100 != 0 || year % 400 == 0));
       if (day>29 || (day==29 && !isleap)) {
          return false;
       }
    }
    else{
       return true;
    }
    return true;
}

function validatedate(inputText, DateFormat) {
    // format dd/mm/yyyy or in any order of (dd or mm or yyyy) you can write dd or mm or yyyy in first or second or third position ... or can be slash"/" or dot"." or dash"-" in the dates formats
    var invalid = "";
    var dt = "";
    var mn = "";
    var yr = "";
    var k;
    var delm = DateFormat.includes("/") ? "/" : ( DateFormat.includes("-") ? "-" : ( DateFormat.includes(".") ? "." : "" ) ) ;
    var f1 = inputText.split(delm);
    var f2 = DateFormat.split(delm);
    for(k=0;k<=2;k++) { 
        dt = dt + (f2[parseInt(k)]=="dd" ? f1[parseInt(k)] : "");
        mn = mn + (f2[parseInt(k)]=="mm" ? f1[parseInt(k)] : "");
        yr = yr + (f2[parseInt(k)]=="yyyy" ? f1[parseInt(k)] : "");
    }
    var mn_days = "0-31-" + (yr % 4 == 0 ? 29 : 28) + "-31-30-31-30-31-31-30-31-30-31";
    var days = mn_days.split("-");
    if (f1.length!=3 ||
    mn.length>2 ||
    dt.length>2 ||
    yr.length!=4 ||
    !(parseInt(mn)>=1 && parseInt(mn)<=12) ||
    !(parseInt(yr)>=parseInt(1900) && parseInt(yr)<=parseInt(2100)) ||
    !(parseInt(dt)>=1 && parseInt(dt)<=parseInt(days[parseInt(mn)]))) {
        invalid = "true";
    }
    alert( ( invalid=="true" ? "Invalid Date" : "Valid Date")  );
}

First string date is converted to js date format and converted into string format again, then it is compared with original string.

function dateValidation(){
    var dateString = "34/05/2019"
    var dateParts = dateString.split("/");
    var date= new Date(+dateParts[2], dateParts[1] - 1, +dateParts[0]);

    var isValid = isValidDate( dateString, date );
    console.log("Is valid date: " + isValid);
}

function isValidDate(dateString, date) {
    var newDateString = ( date.getDate()<10 ? ('0'+date.getDate()) : date.getDate() )+ '/'+ ((date.getMonth() + 1)<10? ('0'+(date.getMonth() + 1)) : (date.getMonth() + 1) )  + '/' +  date.getFullYear();
    return ( dateString == newDateString);
}

var date = new Date(date_string)

returns the literal 'Invalid Date' for any invalid date_string.

Note: Please see the comment's below.

function validatedate(inputText, dateFormat) {
  var minYear = 1950;
  var maxYear = 2050;
  inputText = inputText.toLowerCase();
  if (dateFormat == "dd/mmm/yyyy" || dateFormat == "dd-mmm-yyyy" || dateFormat == "dd.mmm.yyyy" || dateFormat == "dd/yyyy/mmm" || dateFormat == "dd-yyyy-mmm" || dateFormat == "dd.yyyy.mmm" || dateFormat == "mmm/dd/yyyy" || dateFormat == "mmm-dd-yyyy" || dateFormat == "mmm.dd.yyyy" || dateFormat == "mmm/yyyy/dd" || dateFormat == "mmm-yyyy-dd" || dateFormat == "mmm.yyyy.dd" || dateFormat == "yyyy/mmm/dd" || dateFormat == "yyyy-mmm-dd" || dateFormat == "yyyy.mmm.dd" || dateFormat == "yyyy/dd/mmm" || dateFormat == "yyyy-dd-mmm" || dateFormat == "yyyy.dd.mmm") {
    dateFormat = dateFormat.replace("mmm", "mm");
    inputText = inputText.replace("jan", "01");
    inputText = inputText.replace("feb", "02");
    inputText = inputText.replace("mar", "03");
    inputText = inputText.replace("apr", "04");
    inputText = inputText.replace("may", "05");
    inputText = inputText.replace("jun", "06");
    inputText = inputText.replace("jul", "07");
    inputText = inputText.replace("aug", "08");
    inputText = inputText.replace("sep", "09");
    inputText = inputText.replace("oct", "10");
    inputText = inputText.replace("nov", "11");
    inputText = inputText.replace("dec", "12");
  }


  var w;
  var q;
  var delm;
  delm1 = "/";

  for (w = 0; w < inputText.length; w++) {
    q = inputText.charAt(w);
    if (q == '0' || q == '1' || q == '2' || q == '3' || q == '4' || q == '5' || q == '6' || q == '7' || q == '8' || q == '9' || q == '/') {} else {
      delm1 = "";
    }
  }
  delm2 = "-";

  for (w = 0; w < inputText.length; w++) {
    q = inputText.charAt(w);
    if (q == '0' || q == '1' || q == '2' || q == '3' || q == '4' || q == '5' || q == '6' || q == '7' || q == '8' || q == '9' || q == '-') {} else {
      delm2 = "";
    }
  }

  delm3 = ".";

  for (w = 0; w < inputText.length; w++) {
    q = inputText.charAt(w);
    if (q == '0' || q == '1' || q == '2' || q == '3' || q == '4' || q == '5' || q == '6' || q == '7' || q == '8' || q == '9' || q == '.') {} else {
      delm3 = "";
    }
  }

  var delm;
  if (delm1 == "/" && (dateFormat == "dd/mm/yyyy" || dateFormat == "mm/dd/yyyy" || dateFormat == "dd/yyyy/mm" || dateFormat == "mm/yyyy/dd" || dateFormat == "yyyy/mm/dd" || dateFormat == "yyyy/dd/mm")) {
    delm = "/";
  }

  if (delm2 == "-" && (dateFormat == "dd-mm-yyyy" || dateFormat == "mm-dd-yyyy" || dateFormat == "dd-yyyy-mm" || dateFormat == "mm-yyyy-dd" || dateFormat == "yyyy-mm-dd" || dateFormat == "yyyy-dd-mm")) {
    delm = "-";
  }
  if (delm3 == "." && (dateFormat == "dd.mm.yyyy" || dateFormat == "mm.dd.yyyy" || dateFormat == "dd.yyyy.mm" || dateFormat == "mm.yyyy.dd" || dateFormat == "yyyy.mm.dd" || dateFormat == "yyyy.dd.mm")) {
    delm = ".";
  }

  var invalid;
  var f = "31/12/2000";
  f = inputText;
  var ln = f.length;
  var dt;
  var mn;
  var yr;
  var t = f.split(delm);
  var j = t.length;
  if (j == 3) {
    dt = t[0];
    mn = t[1];
    yr = t[2];

    if (dateFormat == "mm.dd.yyyy" || dateFormat == "mm/dd/yyyy" || dateFormat == "mm-dd-yyyy") {
      var tmp = mn;
      mn = dt;
      dt = tmp;
    }

    if (dateFormat == "dd.yyyy.mm" || dateFormat == "dd/yyyy/mm" || dateFormat == "dd-yyyy-mm") {
      var tmp = mn;
      mn = yr;
      yr = tmp;
    }
    if (dateFormat == "mm.yyyy.dd" || dateFormat == "mm/yyyy/dd" || dateFormat == "mm-yyyy-dd") {
      var m1 = mn;
      var d1 = dt;
      var y1 = yr;
      mn = d1;
      yr = m1;
      dt = y1;
    }

    if (dateFormat == "yyyy.mm.dd" || dateFormat == "yyyy/mm/dd" || dateFormat == "yyyy-mm-dd") {
      var m1 = mn;
      var d1 = dt;
      var y1 = yr;
      mn = m1;
      yr = d1;
      dt = y1;
    }

    if (dateFormat == "yyyy.dd.mm" || dateFormat == "yyyy/dd/mm" || dateFormat == "yyyy-dd-mm") {
      var m1 = mn;
      var d1 = dt;
      var y1 = yr;
      mn = y1;
      yr = d1;
      dt = m1;
    }

    if (parseInt(yr) >= parseInt(minYear) && parseInt(yr) <= parseInt(maxYear)) {
      // do nothing
    } else {
      invalid = true;
    }
    if (mn.length > 2) {
      invalid = true;
    }
    if (dt.length > 2) {
      invalid = true;
    }

    if (t[0] == "") {
      invalid = true;
    }
    if (t[1] == "") {
      invalid = true;
    }
    if (t[2] == "") {
      invalid = true;
    }

    if (j != 3) {
      invalid = true;
    }
    var dc;
    var daysArray = "0-31-28-31-30-31-30-31-31-30-31-30-31";

    if ((yr % 4) == 0) {
      daysArray = "0-31-29-31-30-31-30-31-31-30-31-30-31";
    }
    var days = daysArray.split("-");
    if (parseInt(dt) >= 1 && parseInt(dt) <= days[parseInt(mn)]) {} else {
      invalid = true;
    }

    if (yr.length != 4) {
      invalid = true;
    }

    var i;
    var m;

    for (i = 0; i < ln; i++) {
      m = f.charAt(i);
      if (m == '0' || m == '1' || m == '2' || m == '3' || m == '4' || m == '5' || m == '6' || m == '7' || m == '8' || m == '9' || m == delm) {} else {
        invalid = true;
      }
    }
  } else {
    invalid = true;
  }

  console.log(inputText,invalid ? "Invalid Date" : "Valid Date");

}