function changeCoord(id, left) {
 $$(id).style.left = left;
}

function $$(id) {
 return document.getElementById(id);
}

function $$$(id) {
 return document.getElementsByClassName(id)[0];
}

function indexOf(arry, obj) {
 for (var i = 0; i < arry.length; i++) {
  if (obj == arry[i]) {
   return i;
  }
 };
}

window.onload = function() {
 //給頁面上所有的滑塊注冊事件
 //products-box-center 父容器對象

  var obj = document.getElementsByClassName('products-box-center');
  for(var i=0;i<obj.length;i++){
   try{
   var base=obj[i].getElementsByClassName('products-box-center-title')[0]; //取得每一項標題
   var elems=base.getElementsByClassName('products-items-title');
    for(var j=0;j<elems.length;j++){
     var elem=elems[j];
     elem.onmousemove=function(){
      //獲得當前對象的父容器的父容器
      var baseElem=this.parentElement.parentElement;
      var baseIndex=indexOf(obj,baseElem)+1;

      //獲得當前對象的坐標
      var left = this.offsetLeft;

      //獲得對應的滑塊對象
      var slider=$$('products-triangle-'+baseIndex);

      //改變滑塊的坐標
      slider.style.left = left + "px";
      //改變當前對象和其他對象的顏色
      this.style.color = "red";
      //獲取當前父容器下面的所有元素
      var notes=this.parentElement.getElementsByClassName('products-items-title');
      for(var k=0;k<notes.length;k++){
       if(this!=notes[k])
       notes[k].style.color="#666";
      }

     };
    }

   }
   catch(e){
    alert(e);
   }
  };

}

 <div class="products-box-center">
    <div class="products-box-center-title">
     <div class="products-items-title products-focus-text"><h3>最新商品</h3></div>
     <div class="products-items-title"><h3>筆記本</h3></div>
     <div class="products-items-title"><h3>數碼影音</h3></div>
     <div class="products-items-title"><h3>配件</h3></div>
     <div class="products-items-title"><h3>辦公打印</h3></div>
     <div class="products-bottom-triangle" id="products-triangle-${index.count}"><b class="triangle"></b></div>
    </div>

    <div class="products-box-panel">

      <div class="products-item">

       <ul>
        <c:forEach begin="1" end="10">
         <li>
          <a href="#"><img src="img/pc.jpg"/></a>
          <div class="p-name">
           <a href="#">LG IPS237L-BN 23英寸IPS顯示器</a>
          </div>

          <div class="p-price">
           <span>￥1299.00</span>
          </div>

         </li>
        </c:forEach>
       </ul>
      </div>

    </div>

   </div>