Calculating leap year with JS

A simple way to check if the year is a leap year.

[clique aqui para português]

We have a leap year every four years, but it is easy to get confused which year is leap or not, so as not to suffer from it anymore, we will create a new project that finds out if the year is leap or not.

CODE

First we will create the interface, we will do something simple, using only HTML.

HTML code

In the HTML structure an input was created to receive the date we want to know if the year is leap or not, and to give a small increment, we will also find out what day of the week.

Now let’s create the calcularBissexto() function.

JS code — Function countDays

In this function (calcularBissexto()), we have the day_array variable with the days of the week, the date_full variable that receives the date input and we have a function called calcularBissexto which is where we check the date.

The check made in the function calcularBissexto is:

• If year module 4 is 0 AND year module 100 is different from 0 then, leap = true
• If module 400 is 0 then leap = true;
• Any different case then, leap = false;

To find out what day of the week we take the variable date_full and use the standard function getDay() which returns a number value (0–6) and with that value we discover the day of the week day_array[date_full.getDay().

ready as simple as that.

Demo

See the complete project working below.

Project on codepen

Youtube

If you prefer to watch, I see the development on youtube (video in PT-BR).

Video on youtube

Thanks for reading!

If you have any questions, complaints or tips, you can leave them here in the comments. I will be happy to answer!

😊😊See you! 😊😊