文字を一文字ずつフェードインさせながら要素のバックカラーを伸ばす処理(JavaScript)

document.addEventListener('DOMContentLoaded', function() {
	// 一文字ずつ表示
	character_by_character("one-word-box", "one-word-text", 0.5, 0.05 );
	create_a_bar("one-word-box", "one-word-back-box", "one-word-text", 0.5, 0.05 );
	character_by_character("one-word-box2", "one-word-text2", 0.5, 0.05 );
	create_a_bar("one-word-box2", "one-word-back-box2", "one-word-text2", 0.5, 0.05 );
});
// スクロール時の処理
document.addEventListener('DOMContentLoaded', function() {
	window.addEventListener( 'scroll', function() {
		// 一文字ずつ表示
		character_by_character("one-word-box", "one-word-text", 0.5, 0.05 );
		create_a_bar("one-word-box", "one-word-back-box", "one-word-text", 0.5, 0.05 );
		character_by_character("one-word-box2", "one-word-text2", 0.5, 0.05 );
		create_a_bar("one-word-box2", "one-word-back-box2", "one-word-text2", 0.5, 0.05 );
	});
});
//----------------------------------------------------------
// 　文字を一文字ずつ表示させるための処理
//----------------------------------------------------------
function character_by_character( p_idName, t_idName, delay, duration  ) {

  //親の要素を取得
  let p_ele = document.getElementById( p_idName );

  //textのid要素を取得、のち<span>～に書き換える
  let spanText  = document.getElementById( t_idName );

  // 親要要素が見えたら処理
  var scrollTop = window.scrollY;
  var scrollBtm = scrollTop + window.innerHeight

  // 対象の要素の位置を取得
  var targetTop = p_ele.getBoundingClientRect().top + scrollTop;
  var targetBtm =  targetTop + spanText.clientHeight;

  if( scrollBtm > targetTop ) {
      //要素の中身を取得、文字を区切るため
      let text = spanText.innerHTML;
      spanText.style.opacity = 1;

      // すでに<span>に変換してたら処理しない
      if( !(text.indexOf( "span" ) === -1) ) return;

      //変数に空白を設定(spanで上書きする）
      let newText ="";
      let color = "";
    
      //splitで<span>に区切る
      text.split("").forEach(function(value,j) {
          color ="#000000";
          newText += '<span style ="animation:showtext 1s linear ' + ( delay + j*duration  ) + 's forwards; '+ color +' " class ="show">' + value + '</span>';
      });
 
     //spanTextを書き換える
     spanText.innerHTML = newText;
  }
}

//----------------------------------------------------------
// 　横に伸びるバーを作成
//----------------------------------------------------------
function create_a_bar( p_idName, c_idName, t_idName, delay, duration  ) {

  //親の要素を取得
  let p_ele = document.getElementById( p_idName );
  let c_ele = document.getElementById( c_idName );
  let t_ele = document.getElementById( t_idName );
  
  // 親要要素が見えたら処理
  var scrollTop = window.scrollY;
  var scrollBtm = scrollTop + window.innerHeight
    
  // 対象の要素の文字数を取得
  let textLength = t_ele.textContent.length;
  
  // 対象の要素の位置を取得
  var targetTop = p_ele.getBoundingClientRect().top + scrollTop;
  var targetBtm =  targetTop + p_ele.clientHeight;

  if( scrollBtm > targetTop ) {
      // 親要素の高さと横幅を移植
      c_ele.style.transitionDuration = (duration * textLength ) + "s";
      c_ele.style.transitionTimingFunction = "ease-out"
      c_ele.style.transitionDelay =  delay +"s";
      c_ele.style.width = p_ele.clientWidth + "px";
      c_ele.style.height = p_ele.clientHeight + "px";
  }
}

<div id="one-word-box">
<div id="one-word-back-box"></div>
<div id="one-word-text">文字を一文字ずつフェードインさせる処理です</div>
</div>
<div id="one-word-box2">
<div id="one-word-back-box2"></div>
<div id="one-word-text2">同時にバーも伸びる仕様です。2行表示させてます</div>
</div>

#one-word-box, #one-word-box2 {
    position: relative;
    display: block;
    padding: 10px 20px;
	margin: 5px;
    width: fit-content;
    font-weight: 900;
}
#one-word-back-box, #one-word-back-box2 {
    position: absolute;
    top: 0px;
    left: 0px;
    width: 0%;
    height: 100%;
    background-color: #c54747ad;
    transition: all 1s;
    transition-delay: 0s;
    transition-timing-function: liner;
    z-index: 0;
}
#one-word-text, #one-word-text2 {
    opacity: 0;
}
#one-word-text span, #one-word-text2 span {
    font-weight: 900;
    display: inline-block;
    opacity: 0;
}
@keyframes showtext {
    0%{
        opacity: 0;
    }
    100%{
        opacity: 1;
    }
}