JavaScriptのsetTimeout()でページ切り替え時にバウンスボールを表示して切り替え

setTimeout(function(){ 
    element.style.display = "none"; 
  }, 1500);

<div id="page-loading" class="fadein">
  <div class="three-balls">
    <div class="ball ball1"></div>
    <div class="ball ball2"></div>
    <div class="ball ball3"></div>
  </div>
</div>

// bodyタグを取得
const documentBody = document.querySelector('body');
var newElement = document.getElementById("page-loading");

// 2.5秒経ったらオーバーレイ非表示
setTimeout(function(){ 
    newElement.style.display = "none"; 
  }, 2500);

// ページ遷移時にフェードアウト
window.addEventListener("beforeunload", () => {
  documentBody.classList.add('fadeout');
  setTimeout(function(){ 
    documentBody.style.display = "none"; 
  }, 1000);
}, false);

#page-loading {
  position: fixed;
  top: 0;
  left: 0;
  bottom: 0;
  right: 0;
  z-index: 999;
  background-color: #FFF;
  animation : fadeInBounce 2.5s;
  animation-fill-mode: both;
  pointer-events: none;
}
#bounceball {
    position: relative;
    display: block;
    padding: 100px 0 40px;
}

.three-balls {
  margin: 0 auto;
  width: 70px;
  text-align: center;
  position: absolute;
  left: 0;
  right: 0;
  top: 45%;
}

.three-balls .ball {
  position: relative;
  width: 15px;
  height: 15px;
  border-radius: 50%;
  display: inline-block;
  -webkit-animation: bouncedelay 2.0s infinite cubic-bezier(.62, .28, .23, .99) both;
  animation: bouncedelay 2.0s infinite cubic-bezier(.62, .28, .23, .99) both;
}

.three-balls .ball1 {
  -webkit-animation-delay: -.16s;
  animation-delay: -.16s;
}

.three-balls .ball2 {
  -webkit-animation-delay: -.08s;
  animation-delay: -.08s;
}

@keyframes bouncedelay {
  0% {
    bottom: 0;
    background-color: #03A9F4;
  }
  16.66% {
    bottom: 40px;
    background-color: #FB6542;
  }
  33.33% {
    bottom: 0px;
    background-color: #FB6542;
  }
  50% {
    bottom: 40px;
    background-color: #FFBB00;
  }
  66.66% {
    bottom: 0px;
    background-color: #FFBB00;
  }
  83.33% {
    bottom: 40px;
    background-color: #03A9F4;
  }
  100% {
    bottom: 0;
    background-color: #03A9F4;
  }
}

@-webkit-keyframes bouncedelay {
  0% {
    bottom: 0;
    background-color: #03A9F4;
  }
  16.66% {
    bottom: 40px;
    background-color: #FB6542;
  }
  33.33% {
    bottom: 0px;
    background-color: #FB6542;
  }
  50% {
    bottom: 40px;
    background-color: #FFBB00;
  }
  66.66% {
    bottom: 0px;
    background-color: #FFBB00;
  }
  83.33% {
    bottom: 40px;
    background-color: #03A9F4;
  }
  100% {
    bottom: 0;
    background-color: #03A9F4;
  }
}

.fadeout {
  animation : fadeOut 1s;
  animation-fill-mode: both;
}
@keyframes fadeOut {
  0% {
    opacity: 1;
  }
  100% {
    opacity: 0;
  }
}

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