Javascript to animate a countdown. Ideal for a coming soon or event page.

Countdown.js

( function ( ) {
  'use strict';

  function Countdown( endDate, elSelector ) {
    if ( endDate instanceof Date ) {
      this.countdownDate = endDate.getTime( );
    } else {
      this.countdownDate = new Date( endDate ).getTime( );
    }

    var selector = elSelector || Countdown.DEFAULTS.selector;
    this.element = document.querySelector( selector );
    this.intervalId = null;
    this.countdown = this.countdown.bind( this );
  }

  Countdown.SECOND = 1000;
  Countdown.MINUTE = 60 * Countdown.SECOND;
  Countdown.HOUR = 60 * Countdown.MINUTE;
  Countdown.DAY = 24 * Countdown.HOUR;
  Countdown.DEFAULTS = {
    selector: '#countdown-display',
    doneText: "EXPIRED"
  };

  Countdown.prototype.countdown = function ( ) {
    // Get today's date and time
    var now = new Date( ).getTime( );

    // Find the distance between now an the count down date in ms
    var distance = this.countdownDate - now;

    // Time calculations for days, hours, minutes and seconds
    var days = Math.floor( distance / Countdown.DAY ) + 'd';
    var hours = Math.floor( ( distance % Countdown.DAY ) / Countdown.HOUR ) + 'h';
    var minutes = Math.floor( ( distance % Countdown.HOUR ) / Countdown.MINUTE ) + 'm';
    var seconds = Math.floor( ( distance % Countdown.MINUTE ) / Countdown.SECOND ) + 's';

    // Display the result
    this.element.innerHTML = [ days, hours, minutes, seconds ].join( ' ' );

    // If the count down is finished, write the done text
    if ( distance < 0 ) {
      this.stop( );
      this.element.innerHTML = Countdown.DEFAULTS.doneText;
    }

    return this;
  };

  Countdown.prototype.start = function ( ) {
    this.intervalId = window.setInterval( this.countdown, Countdown.SECOND );

    return this;
  };

  Countdown.prototype.stop = function ( ) {
    if ( this.intervalId !== null ) {
      window.clearInterval( this.intervalId );
    }

    return this;
  };

  window.Countdown = Countdown;
}());