GET NUMBER WEEKS WITH JS

geyt-number-weeeks-with-js.js

function parseDate(str) {
    var mdy = str.split('-');
    return new Date(mdy[0], mdy[1]-1, mdy[2]);
}

function datediff(first, second) {
    // Take the difference between the dates and divide by milliseconds per day.
    // Round to nearest whole number to deal with DST.
    return Math.round((second-first)/(1000*60*60*24));
}

let strDateFirt = '2021-01-01';
let strDateSecond = '2021-01-02';
let numberDays = datediff(
  parseDate(strDateFirt),
  parseDate(strDateSecond)
);

let numberWeeks = 0;
if (numberDays >= 7 ){
  numberWeeks = Math.floor( (numberDays/7) );
}

console.log('numberWeeks', numberWeeks);