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CSS

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JavaScript

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Babel includes JSX processing.

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HTML 

              
                <p style="width: 100%; font-size: 20px; line-height: 30px; text-align: center; margin-top: 48vh;">下にスクロールしてみてください。</p>

<div class="fadeAnimation">
  <div class="fadeAnimation__item js-fadeAnimation fadeIn">
    <div class="fadeAnimation__itemInner">
      <p class="fadeAnimation__text">フェードイン</p>
    </div>
  </div><!-- /.fadeAnimation__item -->

  <div class="fadeAnimation__item js-fadeAnimation fadeUp delay04s">
    <div class="fadeAnimation__itemInner">
      <p class="fadeAnimation__text">フェードイン（下から上へ）</p>
    </div>
  </div><!-- /.fadeAnimation__item -->

  <div class="fadeAnimation__item js-fadeAnimation fadeDown delay2s">
    <div class="fadeAnimation__itemInner">
      <p class="fadeAnimation__text">フェードイン（上から下へ）</p>
    </div>
  </div><!-- /.fadeAnimation__item -->

  <div class="fadeAnimation__item js-fadeAnimation fadeRight delay04s">
    <div class="fadeAnimation__itemInner">
      <p class="fadeAnimation__text">フェードイン（左から右へ）</p>
    </div>
  </div><!-- /.fadeAnimation__item -->

  <div class="fadeAnimation__item js-fadeAnimation fadeLeft delay04s">
    <div class="fadeAnimation__itemInner">
      <p class="fadeAnimation__text">フェードイン（右から左へ）</p>
    </div>
  </div><!-- /.fadeAnimation__item -->
</div><!-- /.fadeAnimation -->
!

CSS 

              
                /*------------------------------
 fadeAnimation デモ用装飾
------------------------------*/
.fadeAnimation {
  display: flex;
  flex-flow: row wrap;
  max-width: 96%;
  margin: 60vh auto;
}

.fadeAnimation__item {
  width: 32%;
  height: 40vh;
  background-color: #202f55;
  margin: 0 auto 60vh;
}

.fadeAnimation__itemInner {
  display: table;
  width: 100%;
  height: 100%;
}

.fadeAnimation__text {
  display: table-cell;
  color: #ffffff;
  font-size: 18px;
  text-align: center;
  vertical-align: middle;
  padding: 10px;
  box-sizing: border-box;
}

/*------------------------------
 アニメーション
------------------------------*/
.fadeIn {
  opacity: 0;
}

.fadeUp {
  opacity: 0;
  transform: translateY(50px);
}

.fadeDown {
  opacity: 0;
  transform: translateY(-50%);
}

.fadeRight {
  opacity: 0;
  transform: translateX(-50%);
}

.fadeLeft {
  opacity: 0;
  transform: translateX(50%);
}

.delay01s {
  animation-delay: 0.1s;
}

.delay02s {
  animation-delay: 0.2s;
}

.delay03s {
  animation-delay: 0.3s;
}

.delay04s {
  animation-delay: 0.4s;
}

.delay05s {
  animation-delay: 0.5s;
}

.delay06s {
  animation-delay: 0.6s;
}

.delay07s {
  animation-delay: 0.7s;
}

.delay08s {
  animation-delay: 0.8s;
}

.delay09s {
  animation-delay: 0.9s;
}

.delay1s {
  animation-delay: 1s;
}

.delay2s {
  animation-delay: 2s;
}

.fadeIn.is-animated {
  animation-name: fadeIn;
  animation-duration: 1s;
  animation-fill-mode: both;
}

.fadeUp.is-animated {
  animation-name: fadeUp;
  animation-duration: 1s;
  animation-fill-mode: both;
}

.fadeDown.is-animated {
  animation-name: fadeDown;
  animation-duration: 1s;
  animation-fill-mode: both;
}

.fadeRight.is-animated {
  animation-name: fadeRight;
  animation-duration: 1s;
  animation-fill-mode: both;
}

.fadeLeft.is-animated {
  animation-name: fadeLeft;
  animation-duration: 1s;
  animation-fill-mode: both;
}

@keyframes fadeIn {
  0% {
    opacity: 0;
  }
  100% {
    opacity: 1;
  }
}

@keyframes fadeUp {
  0% {
    opacity: 0;
    transform: translateY(50px);
  }
  100% {
    opacity: 1;
    transform: translateY(0px);
  }
}

@keyframes fadeDown {
  0% {
    opacity: 0;
    transform: translateY(-50px);
  }
  100% {
    opacity: 1;
    transform: translateY(0px);
  }
}

@keyframes fadeRight {
  0% {
    opacity: 0;
    transform: translateX(-50%);
  }
  100% {
    opacity: 1;
    transform: translateX(0px);
  }
}

@keyframes fadeLeft {
  0% {
    opacity: 0;
    transform: translateX(50%);
  }
  100% {
    opacity: 1;
    transform: translateX(0px);
  }
}
!

JS 

              
                // Scroll fade-in animation
(function () { // 即時実行関数（グローバル汚染対策）
  let i = 0; // for文用変数の定義
  let el = {}; // 配列・変数用（巻き上げ防止の為、冒頭にて宣言）

  // DOM読み込み後のタイミングで処理
  document.addEventListener('DOMContentLoaded', function () {
    el.targetElement = document.querySelectorAll('.js-fadeAnimation'); // フェードアニメーション表示させる要素のセレクタ指定
    el.firstDisplayOnlyFlag = false; // フェードアニメーション表示を1回のみにするかの判定フラグ（true：1回のみ、false：複数回）
  }, false);

  // スクロール時の処理
  window.addEventListener('scroll', function () {
    scrollAnimationFnc(); // スクロールアニメーション用関数の実行
  }, false);

  // 向き切り替え（リサイズ）時の処理
  window.addEventListener('resize', function () {
    scrollAnimationFnc(); // スクロールアニメーション用関数の実行
  }, false);

  // スクロールアニメーション用関数
  function scrollAnimationFnc () {
    el.scrollValue = window.pageYOffset || document.documentElement.scrollTop; // 現在のスクロール量の取得
    el.documentHeight = document.documentElement.clientHeight; // ドキュメント全体の高さ（スクロールバー含ない）を取得（表示領域部分の高さ）

    for (i = 0; i < el.targetElement.length; ++i) {
      el.clientRect = el.targetElement[i].getBoundingClientRect(); // 対象要素のViewpor（ビューポート）に対する相対位置に関する情報を取得
      el.targetPosition = el.clientRect.top + el.scrollValue; // 対象要素の位置座標を取得
      el.targetHeight = el.targetElement[i].offsetHeight; // 対象要素のborder、paddingを含んだ高さを取得

      if (el.scrollValue < el.targetPosition - el.documentHeight || el.scrollValue > el.targetPosition + el.targetHeight) {
        // ドキュメント全体の高さ（スクロールバー含ない）内（表示領域）に対象要素の位置が入っていなければ処理
        if (!el.firstDisplayOnlyFlag) {
          // 判定フラグが「false（複数回）」の場合に処理
          el.targetElement[i].classList.remove('is-animated'); // 対象要素から「is-animated」classを削除する
        } else {
          // 判定フラグが「true（1回のみ）」の場合に処理
          return false; // 処理を中断
        }
      } else {
        // ドキュメント全体の高さ（スクロールバー含ない）内（表示領域）に対象要素の位置が入っていれば処理
        el.targetElement[i].classList.add('is-animated'); // 対象要素に「is-animated」classを付与する
      }
    }
  }
}());
!
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