How to validate a date?

Question

I'm trying to test to make sure a date is valid in the sense that if someone enters 2/30/2011 then it should be wrong.

How can I do this with any date?

Answer 1

One simple way to validate a date string is to convert to a date object and test that, e.g.

// Expect input as d/m/y  function isValidDate(s) {    var bits = s.split('/');    var d = new Date(bits[2], bits[1] - 1, bits[0]);    return d && (d.getMonth() + 1) == bits[1];  }    ['0/10/2017','29/2/2016','01/02'].forEach(function(s) {    console.log(s + ' : ' + isValidDate(s))  })

When testing a Date this way, only the month needs to be tested since if the date is out of range, the month will change. Same if the month is out of range. Any year is valid.

You can also test the bits of the date string:

function isValidDate2(s) {    var bits = s.split('/');    var y = bits[2],      m = bits[1],      d = bits[0];    // Assume not leap year by default (note zero index for Jan)    var daysInMonth = [31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31];      // If evenly divisible by 4 and not evenly divisible by 100,    // or is evenly divisible by 400, then a leap year    if ((!(y % 4) && y % 100) || !(y % 400)) {      daysInMonth[1] = 29;    }    return !(/\D/.test(String(d))) && d > 0 && d <= daysInMonth[--m]  }    ['0/10/2017','29/2/2016','01/02'].forEach(function(s) {    console.log(s + ' : ' + isValidDate2(s))  })

Answer 2

Does first function isValidDate(s) proposed by RobG will work for input string '1/2/'? I think NOT, because the YEAR is not validated ;(

My proposition is to use improved version of this function:

//input in ISO format: yyyy-MM-dd function DatePicker_IsValidDate(input) {         var bits = input.split('-');         var d = new Date(bits[0], bits[1] - 1, bits[2]);         return d.getFullYear() == bits[0] && (d.getMonth() + 1) == bits[1] && d.getDate() == Number(bits[2]); }