JSFiddle - React, Tailwind, and code Playground

JavaScript

function getDateDiff(date1, date2) {
    return date2.getTime() - date1.getTime();
}

function getSunday(date) {
    var newDate = new Date(date);
    newDate.setDate(date.getDate() - date.getDay());
    newDate.setHours(0, 0, 0, 0);
    return newDate;
}

var date = new Date(2016, 5, 18, 13, 30, 0, 0); // 2016/06/18 at 1:30PM

console.log(date);
console.log(getSunday(date));

var diff = getDateDiff(getSunday(date), date);

console.log(diff);

var hourDiff = Math.floor(diff/1000/60/60);

console.log(hourDiff);