【jQuery】固定した背景画像がスクロールで切り替わる実装サンプル（スマホでも切り替わります）

スクロールすると固定した背景画像が切り替わる実装サンプルをまとめてみました。
CSSだけで対応できると素敵なのですが『background-attachment: fixed;』がスマホだと効かないので、今回はjQueryを使って実装してみました。

おしゃれなサイトでよく見かけますねー

おしゃれなサイト増えましたよねー

実装サンプル

See the Pen 【CSS + jQuery】Fixed background full sections (Responsive) by 125naroom (@125naroom) on CodePen.

HTMLとCSSとjQueryはこちら

HTML

<main>
  <section>
    <div class="one">
      <div class="bg _01"></div>
      <div class="onebox">
        <img src="https://125naroom.com/demo/img/itukanokotonokoto01.jpg" alt="">
        <p>1st</p>
      </div>
    </div>
  </section>
  <section>
    <div class="one">
      <div class="bg _02"></div>
      <div class="onebox">
        <img src="https://125naroom.com/demo/img/itukanokotonokoto02.jpg" alt="">
        <p>2nd</p>
      </div>
    </div>
  </section>
  <section>
    <div class="one">
      <div class="bg _03"></div>
      <div class="onebox">
        <img src="https://125naroom.com/demo/img/itukanokotonokoto03.jpg" alt="">
        <p>3rd</p>
      </div>
    </div>
  </section>
  <section>
    <div class="one">
      <div class="bg _04"></div>
      <div class="onebox">
        <img src="https://125naroom.com/demo/img/itukanokotonokoto04.jpg" alt="">
        <p>4th</p>
      </div>
    </div>
  </section>
  <section>
    <div class="one">
      <div class="bg _05"></div>
      <div class="onebox">
        <img src="https://125naroom.com/demo/img/itukanokotonokoto05.jpg" alt="">
        <p>5th</p>
      </div>
    </div>
  </section>
</main>

CSS

display: none;とdisplay: block;がポイントです。

section {
    display: flex;
}
.one {
    display: flex;
    align-items: center;
    width: 100%;
    min-height: 100vh;
    padding: 20px;
}
.bg {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    width: 100%;
    height: 100%;
    background-position: center center;
    background-size: cover;
    background-repeat: no-repeat;
    display: none;
    z-index: -1;
}
.show .bg {
    display: block;
}
.bg._01 {
    background-image: url("https://125naroom.com/demo/img/itukanokotonokoto01.jpg");
}
.bg._02 {
    background-image: url("https://125naroom.com/demo/img/itukanokotonokoto02.jpg");
}
.bg._03 {
    background-image: url("https://125naroom.com/demo/img/itukanokotonokoto03.jpg");
}
.bg._04 {
    background-image: url("https://125naroom.com/demo/img/itukanokotonokoto04.jpg");
}
.bg._05 {
    background-image: url("https://125naroom.com/demo/img/itukanokotonokoto05.jpg");
}
.onebox {
    max-width: 400px;
    margin: 0 auto;
    padding: 20px;
    background: #ffffff;
}
.onebox img {
    width: 100%;
    height: auto;
    vertical-align: top;
    margin-bottom: 15px;
}
.onebox p {
    text-align: center;
    margin: 0;
}

jQuery

コンテンツが50px見えたらクラスが付与します。

$(function(){
  $(".one").each(function(i, elem){
    var one = $(elem).offset().top;
    $(window).on("load scroll resize", function(){
      var two = $(window).height();
      var three = $(window).scrollTop();
      var showClass = "show";
      var timing = 50; // 50px, add to css
      if (three >= one - two + timing){
        $(elem).addClass(showClass);
      } else {
        $(elem).removeClass(showClass);
      }
    });
  });
});

サンプルページはこちら

実装サンプル（フェードイン効果をつけてみる）

See the Pen 【CSS + jQuery】Fixed background full sections + fade-in (Responsive) by 125naroom (@125naroom) on CodePen.

HTMLとCSSとjQueryはこちら

HTML

<main>
  <section>
    <div class="one">
      <div class="bg _01"></div>
      <div class="onebox">
        <img src="https://125naroom.com/demo/img/itukanokotonokoto01.jpg" alt="">
        <p>1st</p>
      </div>
    </div>
  </section>
  <section>
    <div class="one">
      <div class="bg _02"></div>
      <div class="onebox">
        <img src="https://125naroom.com/demo/img/itukanokotonokoto02.jpg" alt="">
        <p>2nd</p>
      </div>
    </div>
  </section>
  <section>
    <div class="one">
      <div class="bg _03"></div>
      <div class="onebox">
        <img src="https://125naroom.com/demo/img/itukanokotonokoto03.jpg" alt="">
        <p>3rd</p>
      </div>
    </div>
  </section>
  <section>
    <div class="one">
      <div class="bg _04"></div>
      <div class="onebox">
        <img src="https://125naroom.com/demo/img/itukanokotonokoto04.jpg" alt="">
        <p>4th</p>
      </div>
    </div>
  </section>
  <section>
    <div class="one">
      <div class="bg _05"></div>
      <div class="onebox">
        <img src="https://125naroom.com/demo/img/itukanokotonokoto05.jpg" alt="">
        <p>5th</p>
      </div>
    </div>
  </section>
</main>

CSS

transitionとopacityで効果をつけました。

section {
    display: flex;
}
.one {
    display: flex;
    align-items: center;
    width: 100%;
    min-height: 100vh;
    padding: 20px;
}
.bg {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    width: 100%;
    height: 100%;
    background-position: center center;
    background-size: cover;
    background-repeat: no-repeat;
    opacity: 0;
    transition: all 0.5s ease 0s;
    z-index: -1;
}
.show .bg {
    opacity: 1;
}
.bg._01 {
    background-image: url("https://125naroom.com/demo/img/itukanokotonokoto01.jpg");
}
.bg._02 {
    background-image: url("https://125naroom.com/demo/img/itukanokotonokoto02.jpg");
}
.bg._03 {
    background-image: url("https://125naroom.com/demo/img/itukanokotonokoto03.jpg");
}
.bg._04 {
    background-image: url("https://125naroom.com/demo/img/itukanokotonokoto04.jpg");
}
.bg._05 {
    background-image: url("https://125naroom.com/demo/img/itukanokotonokoto05.jpg");
}
.onebox {
    max-width: 400px;
    margin: 0 auto;
    padding: 20px;
    background: #ffffff;
}
.onebox img {
    width: 100%;
    height: auto;
    vertical-align: top;
    margin-bottom: 15px;
}
.onebox p {
    text-align: center;
    margin: 0;
}

jQuery

コンテンツが50px見えたらクラスが付与します。

$(function(){
  $(".one").each(function(i, elem){
    var one = $(elem).offset().top;
    $(window).on("load scroll resize", function(){
      var two = $(window).height();
      var three = $(window).scrollTop();
      var showClass = "show";
      var timing = 50; // 50px, add to css
      if (three >= one - two + timing){
        $(elem).addClass(showClass);
      } else {
        $(elem).removeClass(showClass);
      }
    });
  });
});

サンプルページはこちら