JSFiddle - React, Tailwind, and code Playground

JavaScript

var decalage = +1
var decalage_minute = 30

var d = new Date(); //date
		
//convert date timestamp
function heure_decalage_f(date, decalage){
    var data = new Date(date.getTime() + (decalage * 60 * 60 * 1e3));
    return data.getHours();
}

function minute_decalage_f(date, decalage){
    var data = new Date(date.getTime() + (decalage * 60 * 1e3));
    return data.getMinutes();
}

var heure_decalage = heure_decalage_f(d,decalage);
var minute_dec     = minute_decalage_f(d,decalage_minute);

var minute = d.getMinutes();
var seconds = d.getSeconds();
var hour = d.getHours();

alert(heure_decalage + ":" + minute);
alert(hour + ":" + minute_dec);