### How to validate number of days in a given month with JavaScript?

Sometimes, we want to validate number of days in a given month with JavaScript.

In this article, we’ll look at how to validate number of days in a given month with JavaScript.

### How to validate number of days in a given month with JavaScript?

To validate number of days in a given month with JavaScript, we can write our own function to check the number of days of a given month.

For instance, we write:

``````const daysInMonth = (m, y) => {
switch (m) {
case 1:
return (y % 4 == 0 && y % 100) || y % 400 == 0 ? 29 : 28;
case 8:
case 3:
case 5:
case 10:
return 30;
default:
return 31
}
}

const isValid = (d, m, y) => {
return m >= 0 && m < 12 && d > 0 && d <= daysInMonth(m, y);
}

console.log(isValid(20, 1, 2022))
console.log(isValid(30, 1, 2022))
``````

to define the `daysInMonth` function that takes month `m` and year `y` as parameters.

`m` is between 0 and 11 where 0 is January and 11 is December.

In the function, we check if February is in a leap year.

If it is, 23 return 29 and 28 otherwise.

For the other months, we check whether the month has 30 or 31 days.

Then we define the `isValid` function that takes day `d`, month `m` and year `y`.

In the function, we check if `m` is between 0 and 11, and `d` is in the valid range for the month.

Therefore, the first log is `true` and the 2nd is `false`.

### Conclusion

To validate number of days in a given month with JavaScript, we can write our own function to check the number of days of a given month.