Date.getDate()

Date.getFullYear()

Date.getMonth()

function daysInMonth(month, year) {
    return new Date(year, month, 0).getDate();
}
 
function GFG_Fun() {
    let date = new Date();
    let month = 2;
    let year = 2020;
    console.log("Number of days in " + month
        + "and month of the year " + year
        + " is " + daysInMonth(month, year));
}
GFG_Fun()

Number of days in 2and month of the year 2020 is 29

function daysInMonth(month, year) {
    return new Date(year, month, 0).getDate();
}
 
function GFG_Fun() {
    let date = new Date();
    let month = date.getMonth() + 1;
    let year = date.getFullYear();
    console.log("Number of days in " + month
        + "th month of the year " + year
        + " is " + daysInMonth(month, year));
}
GFG_Fun()

Number of days in 6th month of the year 2023 is 30