HTML редактор

<!DOCTYPE html>
<html lang="ru">

<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
  <title>JavaScript - Как сделать слайдер для сайта</title>
  <style>
    /*!
     * chiefSlider (https://itchief.ru/lessons/php/feedback-form-for-website)
     * Copyright 2018 Alexander Maltsev
     * Licensed under MIT (https://github.com/itchief/feedback-form/blob/master/LICENSE)
     */

body {
      margin: 0;
      font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol";
      color: #fff;
      height: 3000px;
    }

.slider {
      position: relative;
      overflow: hidden;
    }

.slider__wrapper {
      display: flex;
      transition: transform 0.6s ease;
    }

.slider__item {
      flex: 0 0 33.333333%;
      max-width: 33.333333%;
    }

.slider__control {
      position: absolute;
      top: 50%;
      display: none;
      align-items: center;
      justify-content: center;
      width: 40px;
      color: #fff;
      text-align: center;
      opacity: 0.5;
      height: 50px;
      transform: translateY(-50%);
      background: rgba(0, 0, 0, .5);
    }

.slider__control_show {
      display: flex;
    }

.slider__control:hover,
    .slider__control:focus {
      color: #fff;
      text-decoration: none;
      outline: 0;
      opacity: .9;
    }

.slider__control_left {
      left: 0;
    }

.slider__control_right {
      right: 0;
    }

.slider__control::before {
      content: '';
      display: inline-block;
      width: 20px;
      height: 20px;
      background: transparent no-repeat center center;
      background-size: 100% 100%;
    }

.slider__control_left::before {
      background-image: url("data:image/svg+xml;charset=utf8,%3Csvg xmlns='http://www.w3.org/2000/svg' fill='%23fff' viewBox='0 0 8 8'%3E%3Cpath d='M5.25 0l-4 4 4 4 1.5-1.5-2.5-2.5 2.5-2.5-1.5-1.5z'/%3E%3C/svg%3E");
    }

.slider__control_right::before {
      background-image: url("data:image/svg+xml;charset=utf8,%3Csvg xmlns='http://www.w3.org/2000/svg' fill='%23fff' viewBox='0 0 8 8'%3E%3Cpath d='M2.75 0l-1.5 1.5 2.5 2.5-2.5 2.5 1.5 1.5 4-4-4-4z'/%3E%3C/svg%3E");
    }

.slider__item>div {
      line-height: 250px;
      font-size: 100px;
      text-align: center;
    }
  </style>
</head>

<body>

var position = {
          getMin: 0,
          getMax: _items.length - 1,
        }

// обработчик события click для кнопок "назад" и "вперед"
        var _controlClick = function (e) {
          if (e.target.classList.contains('slider__control')) {
            e.preventDefault();
            var direction = e.target.classList.contains('slider__control_right') ? 'right' : 'left';
            _transformItem(direction);
          }
        };

var _setUpListeners = function () {
          // добавление к кнопкам "назад" и "вперед" обрботчика _controlClick для событя click
          _sliderControls.forEach(function (item) {
            item.addEventListener('click', _controlClick);
          });
        }

// инициализация
        _setUpListeners();

return {
          right: function () { // метод right
            _transformItem('right');
          },
          left: function () { // метод left
            _transformItem('left');
          }
        }

}
    }());

var slider = multiItemSlider('.slider')

</script>

</body>

</html>