JavaScript validate date and return last available date of calendar

Question

I want to validate my date if date not exits in calendar then return me last available date of calendar,

Example 01

Input Date    : 31         


        

Answer 1

You can try something like this:

Explanation as per spec:

When we call date constructor with 2 or more arguments, it tries to process using following constructor ref:

new Date (year, month [, date [, hours [, minutes [, seconds [, ms ] ] ] ] ] )

Here if any value that is not passed, it will be set as NaN and later will be parsed to +0. Hence timestamp is 0:0:0

Now the trick is in a function called internally: MakeDay.

As you see point 8, it returns

Day(t) + dt − 1

Here Day(t) would return number of milliseconds and date would be calculated based on dt - 1. Since we are passing 0, date value would be -1 + milliseconds and hence it returns previous day.

Another alternate would be to create date for 1st of next month and subtract 1 as day or sec. You can select anyone based on the need,

function isValidDate(year, month, day) {
  var d = new Date(year, month, day);
  return !!(d.getFullYear() == year && d.getMonth() == month && d.getDate() == day)
}

function computeLastPossibleDate(y,m,d){
  return new Date(y, m+1, 0);
}

function test(y,m,d){
  return isValidDate(y,m,d) ? new Date(y,m,d) : computeLastPossibleDate(y,m,d)
}

// 31st Feb.
console.log(test(2017, 1, 31).toString())
// 31st March
console.log(test(2017, 2, 31).toString())
// 31st April
console.log(test(2017, 3, 31).toString())
// 50th Dec.
console.log(test(2017, 11, 50).toString())

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