JSFiddle - React, Tailwind, and code Playground

HTML

до первого апреля <span id="first"></span>

<h1>НОВЫЙ ГОД ЧЕРЕЗ <span id="newyear"></span></h1>

таймер на минуту: <span id="min"></span>

JavaScript

function countdown(dateStr, display) {
  let targetDate = new Date(dateStr).getTime(),
      timer = setInterval(function() {
        let now = new Date().getTime(),
            diff = targetDate - now;

        let days = Math.floor(diff / 86400000),
            hours = Math.floor((diff % 86400000) / 3600000),
            minutes = Math.floor((diff % 3600000) / 60000),
            seconds = Math.floor((diff % 60000) / 1000);

        display.innerHTML = days + " дней " + hours + "ч "
          + minutes + "м " + seconds + "с ";

        if (diff < 0) {
          clearInterval(timer);
          display.innerHTML = "ура, дождались";
        }
      }, 1000);
}

var display = document.getElementById('first')
countdown('2018-04-01 00:00:00', display)

display = document.getElementById('newyear')
countdown('2018 GMT+0300', display)

countdown(new Date().getTime()+60000, min)